xref: /open-nvidia-gpu/kernel-open/nvidia-uvm/uvm_perf_thrashing.c (revision b5bf85a8)

/*******************************************************************************
    Copyright (c) 2016-2023 NVIDIA Corporation

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    of this software and associated documentation files (the "Software"), to
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#include "uvm_api.h"
#include "uvm_conf_computing.h"
#include "uvm_perf_events.h"
#include "uvm_perf_module.h"
#include "uvm_perf_thrashing.h"
#include "uvm_perf_utils.h"
#include "uvm_va_block.h"
#include "uvm_va_range.h"
#include "uvm_kvmalloc.h"
#include "uvm_tools.h"
#include "uvm_procfs.h"
#include "uvm_test.h"

// Number of bits for page-granularity time stamps. Currently we ignore the first 6 bits
// of the timestamp (i.e. we have 64ns resolution, which is good enough)
#define PAGE_THRASHING_LAST_TIME_STAMP_BITS 58
#define PAGE_THRASHING_NUM_EVENTS_BITS      3

#define PAGE_THRASHING_THROTTLING_END_TIME_STAMP_BITS 58
#define PAGE_THRASHING_THROTTLING_COUNT_BITS          8

// Per-page thrashing detection structure.
typedef struct
{
    struct
    {
        // Last time stamp when a thrashing-related event was recorded
        NvU64                        last_time_stamp : PAGE_THRASHING_LAST_TIME_STAMP_BITS;

        bool                    has_migration_events : 1;

        bool                   has_revocation_events : 1;

        // Number of consecutive "thrashing" events (within the configured
        // thrashing lapse)
        NvU8                    num_thrashing_events : PAGE_THRASHING_NUM_EVENTS_BITS;

        bool                                  pinned : 1;
    };

    struct
    {
        // Deadline for throttled processors to wake up
        NvU64              throttling_end_time_stamp : PAGE_THRASHING_THROTTLING_END_TIME_STAMP_BITS;

        // Number of times a processor has been throttled. This is used to
        // determine when the page needs to get pinned. After getting pinned
        // this field is always 0.
        NvU8                        throttling_count : PAGE_THRASHING_THROTTLING_COUNT_BITS;
    };

    // Processors accessing this page
    uvm_processor_mask_t                  processors;

    // Processors that have been throttled. This must be a subset of processors
    uvm_processor_mask_t        throttled_processors;

    // Memory residency for the page when in pinning phase
    uvm_processor_id_t           pinned_residency_id;

    // Processor not to be throttled in the current throttling period
    uvm_processor_id_t  do_not_throttle_processor_id;
} page_thrashing_info_t;

// Per-VA block thrashing detection structure. This state is protected by the
// VA block lock.
typedef struct
{
    page_thrashing_info_t                     *pages;

    NvU16                        num_thrashing_pages;

    NvU8                       thrashing_reset_count;

    uvm_processor_id_t                last_processor;

    NvU64                            last_time_stamp;

    NvU64                  last_thrashing_time_stamp;

    // Stats
    NvU32                           throttling_count;

    uvm_page_mask_t                  thrashing_pages;

    struct
    {
        NvU32                                  count;

        uvm_page_mask_t                         mask;

        // List of pinned pages. This list is only used if the pinning timeout
        // is not 0.
        struct list_head                        list;
    } pinned_pages;
} block_thrashing_info_t;

// Descriptor for a page that has been pinned due to thrashing. This structure
// is only used if the pinning timeout is not 0.
typedef struct
{
    uvm_va_block_t                         *va_block;

    // Page index within va_block
    uvm_page_index_t                      page_index;

    // Absolute timestamp after which the page will be unpinned
    NvU64                                   deadline;

    // Entry in the per-VA Space list of pinned pages. See
    // va_space_thrashing_info_t::pinned_pages::list.
    struct list_head             va_space_list_entry;

    // Entry in the per-VA Block list of pinned pages. See
    // block_thrashing_info_t::pinned_pages::list.
    struct list_head             va_block_list_entry;
} pinned_page_t;

// Per-VA space data structures and policy configuration
typedef struct
{
    // Per-VA space accounting of pinned pages that is used to speculatively
    // unpin pages after the configured timeout. This struct is only used if
    // the pinning timeout is not 0.
    struct
    {
        // Work descriptor that is executed asynchronously by a helper thread
        struct delayed_work                    dwork;

        // List of pinned pages. They are (mostly) ordered by unpin deadline.
        // New entries are inserted blindly at the tail since the expectation
        // is that they will have the largest deadline value. However, given
        // the drift between when multiple threads query their timestamps and
        // add those pages to the list under the lock, it might not be
        // strictly ordered. But this is OK since the difference will be very
        // small and they will be eventually removed from the list.
        //
        // Entries are removed when they reach the deadline by the function
        // configured in dwork. This list is protected by lock.
        struct list_head                        list;

        uvm_spinlock_t                          lock;

        uvm_va_block_context_t      *va_block_context;

        // Flag used to avoid scheduling delayed unpinning operations after
        // uvm_perf_thrashing_stop has been called.
        bool                    in_va_space_teardown;
    } pinned_pages;

    struct
    {
        // Whether thrashing mitigation is enabled on this VA space
        bool                                  enable;

        // true if the thrashing mitigation parameters have been modified using
        // test ioctls
        bool                          test_overrides;

        //
        // Fields below are the thrashing mitigation parameters on the VA space
        //
        unsigned                           threshold;

        unsigned                       pin_threshold;

        NvU64                               lapse_ns;

        NvU64                                 nap_ns;

        NvU64                               epoch_ns;

        unsigned                          max_resets;

        NvU64                                 pin_ns;
    } params;

    uvm_va_space_t                         *va_space;
} va_space_thrashing_info_t;

typedef struct
{
    // Entry for the per-processor thrashing_stats file in procfs
    struct proc_dir_entry *procfs_file;

    // Number of times thrashing is detected
    atomic64_t num_thrashing;

    // Number of times the processor was throttled while thrashing
    atomic64_t num_throttle;

    // Number of times a page was pinned on this processor while thrashing
    atomic64_t num_pin_local;

    // Number of times a page was pinned on a different processor while thrashing
    atomic64_t num_pin_remote;
} processor_thrashing_stats_t;

// Pre-allocated thrashing stats structure for the CPU. This is only valid if
// uvm_procfs_is_debug_enabled() returns true.
static processor_thrashing_stats_t g_cpu_thrashing_stats;

#define PROCESSOR_THRASHING_STATS_INC(va_space, proc, field)                                         \
    do {                                                                                             \
        processor_thrashing_stats_t *_processor_stats = thrashing_stats_get_or_null(va_space, proc); \
        if (_processor_stats)                                                                        \
            atomic64_inc(&_processor_stats->field);                                                  \
    } while (0)

// Global caches for the per-VA block thrashing detection structures
static struct kmem_cache *g_va_block_thrashing_info_cache __read_mostly;
static struct kmem_cache *g_pinned_page_cache __read_mostly;

//
// Tunables for thrashing detection/prevention (configurable via module parameters)
//

#define UVM_PERF_THRASHING_ENABLE_DEFAULT 1

// Enable/disable thrashing performance heuristics
static unsigned uvm_perf_thrashing_enable = UVM_PERF_THRASHING_ENABLE_DEFAULT;

#define UVM_PERF_THRASHING_THRESHOLD_DEFAULT 3
#define UVM_PERF_THRASHING_THRESHOLD_MAX     ((1 << PAGE_THRASHING_NUM_EVENTS_BITS) - 1)

// Number of consecutive thrashing events to initiate thrashing prevention
//
// Maximum value is UVM_PERF_THRASHING_THRESHOLD_MAX
static unsigned uvm_perf_thrashing_threshold = UVM_PERF_THRASHING_THRESHOLD_DEFAULT;

#define UVM_PERF_THRASHING_PIN_THRESHOLD_DEFAULT 10
#define UVM_PERF_THRASHING_PIN_THRESHOLD_MAX     ((1 << PAGE_THRASHING_THROTTLING_COUNT_BITS) - 1)

// Number of consecutive throttling operations before trying to map remotely
//
// Maximum value is UVM_PERF_THRASHING_PIN_THRESHOLD_MAX
static unsigned uvm_perf_thrashing_pin_threshold = UVM_PERF_THRASHING_PIN_THRESHOLD_DEFAULT;

// TODO: Bug 1768615: [uvm] Automatically tune default values for thrashing
// detection/prevention parameters
#define UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT 500
#define UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT_EMULATION (UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT * 800)
#define UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT_HCC (UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT * 10)

// Lapse of time in microseconds that determines if two consecutive events on
// the same page can be considered thrashing
static unsigned uvm_perf_thrashing_lapse_usec = UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT;

#define UVM_PERF_THRASHING_NAP_DEFAULT 1
#define UVM_PERF_THRASHING_NAP_MAX     100

// Time that the processor being throttled is forbidden to work on the thrashing
// page. This value is a multiplier of uvm_perf_thrashing_lapse_usec.
static unsigned uvm_perf_thrashing_nap = UVM_PERF_THRASHING_NAP_DEFAULT;

#define UVM_PERF_THRASHING_EPOCH_DEFAULT 2000

// Time lapse after which we consider thrashing is no longer happening. This
// value is a multiplier of uvm_perf_thrashing_lapse_usec.
static unsigned uvm_perf_thrashing_epoch = UVM_PERF_THRASHING_EPOCH_DEFAULT;

// When pages are pinned and the rest of thrashing processors are mapped
// remotely we lose track of who is accessing the page for the rest of
// program execution. This can lead to tremendous performance loss if the page
// is not thrashing anymore and it is always being accessed remotely.
// In order to avoid that scenario, we use a timer that unpins memory after
// some time. We use a per-VA space list of pinned pages, sorted by the
// deadline at which it will be unmapped from remote processors. Therefore,
// next remote access will trigger a fault that will migrate the page.
#define UVM_PERF_THRASHING_PIN_DEFAULT 300
#define UVM_PERF_THRASHING_PIN_DEFAULT_EMULATION 10

// Time for which a page remains pinned. This value is a multiplier of
// uvm_perf_thrashing_lapse_usec. 0 means that it is pinned forever.
static unsigned uvm_perf_thrashing_pin = UVM_PERF_THRASHING_PIN_DEFAULT;

// Number of times a VA block can be reset back to non-thrashing. This
// mechanism tries to avoid performing optimizations on a block that periodically
// causes thrashing
#define UVM_PERF_THRASHING_MAX_RESETS_DEFAULT 4

static unsigned uvm_perf_thrashing_max_resets = UVM_PERF_THRASHING_MAX_RESETS_DEFAULT;

// Module parameters for the tunables
module_param(uvm_perf_thrashing_enable,        uint, S_IRUGO);
module_param(uvm_perf_thrashing_threshold,     uint, S_IRUGO);
module_param(uvm_perf_thrashing_pin_threshold, uint, S_IRUGO);
module_param(uvm_perf_thrashing_lapse_usec,    uint, S_IRUGO);
module_param(uvm_perf_thrashing_nap,           uint, S_IRUGO);
module_param(uvm_perf_thrashing_epoch,         uint, S_IRUGO);
module_param(uvm_perf_thrashing_pin,           uint, S_IRUGO);
module_param(uvm_perf_thrashing_max_resets,    uint, S_IRUGO);

// See map_remote_on_atomic_fault uvm_va_block.c
unsigned uvm_perf_map_remote_on_native_atomics_fault = 0;
module_param(uvm_perf_map_remote_on_native_atomics_fault, uint, S_IRUGO);

// Global post-processed values of the module parameters. They can be overriden
// per VA-space.
static bool g_uvm_perf_thrashing_enable;
static unsigned g_uvm_perf_thrashing_threshold;
static unsigned g_uvm_perf_thrashing_pin_threshold;
static NvU64 g_uvm_perf_thrashing_lapse_usec;
static NvU64 g_uvm_perf_thrashing_nap;
static NvU64 g_uvm_perf_thrashing_epoch;
static NvU64 g_uvm_perf_thrashing_pin;
static unsigned g_uvm_perf_thrashing_max_resets;

// Helper macros to initialize thrashing parameters from module parameters
//
// This helper returns whether the type for the parameter is signed
#define THRASHING_PARAMETER_IS_SIGNED(v) (((typeof(v)) -1) < 0)

// Macro that initializes the given thrashing parameter and checks its validity
// (within [_mi:_ma]). Otherwise it is initialized with the given default
// parameter _d. The user value is read from _v, and the final value is stored
// in a variable named g_##_v, so it must be declared, too. Only unsigned
// parameters are supported.
#define INIT_THRASHING_PARAMETER_MIN_MAX(_v, _d, _mi, _ma)                      \
    do {                                                                        \
        unsigned v = (_v);                                                      \
        unsigned d = (_d);                                                      \
        unsigned mi = (_mi);                                                    \
        unsigned ma = (_ma);                                                    \
                                                                                \
        BUILD_BUG_ON(sizeof(_v) > sizeof(unsigned));                            \
        BUILD_BUG_ON(THRASHING_PARAMETER_IS_SIGNED(_v));                        \
                                                                                \
        UVM_ASSERT(mi <= ma);                                                   \
        UVM_ASSERT(d >= mi);                                                    \
        UVM_ASSERT(d <= ma);                                                    \
                                                                                \
        if (v >= mi && v <= ma) {                                               \
            g_##_v = v;                                                         \
        }                                                                       \
        else {                                                                  \
            pr_info("Invalid value %u for " #_v ". Using %u instead\n", v, d);  \
                                                                                \
            g_##_v = d;                                                         \
        }                                                                       \
    } while (0)

#define INIT_THRASHING_PARAMETER(v, d)                 INIT_THRASHING_PARAMETER_MIN_MAX(v, d, 0u, UINT_MAX)

#define INIT_THRASHING_PARAMETER_MIN(v, d, mi)         INIT_THRASHING_PARAMETER_MIN_MAX(v, d, mi, UINT_MAX)
#define INIT_THRASHING_PARAMETER_MAX(v, d, ma)         INIT_THRASHING_PARAMETER_MIN_MAX(v, d, 0u, ma)

#define INIT_THRASHING_PARAMETER_NONZERO(v, d)         INIT_THRASHING_PARAMETER_MIN_MAX(v, d, 1u, UINT_MAX)
#define INIT_THRASHING_PARAMETER_NONZERO_MAX(v, d, ma) INIT_THRASHING_PARAMETER_MIN_MAX(v, d, 1u, ma)

#define INIT_THRASHING_PARAMETER_TOGGLE(v, d)          INIT_THRASHING_PARAMETER_MIN_MAX(v, d, 0u, 1u)

// Helpers to get/set the time stamp
static NvU64 page_thrashing_get_time_stamp(page_thrashing_info_t *entry)
{
    return entry->last_time_stamp << (64 - PAGE_THRASHING_LAST_TIME_STAMP_BITS);
}

static void page_thrashing_set_time_stamp(page_thrashing_info_t *entry, NvU64 time_stamp)
{
    entry->last_time_stamp = time_stamp >> (64 - PAGE_THRASHING_LAST_TIME_STAMP_BITS);
}

static NvU64 page_thrashing_get_throttling_end_time_stamp(page_thrashing_info_t *entry)
{
    return entry->throttling_end_time_stamp << (64 - PAGE_THRASHING_THROTTLING_END_TIME_STAMP_BITS);
}

static void page_thrashing_set_throttling_end_time_stamp(page_thrashing_info_t *entry, NvU64 time_stamp)
{
    entry->throttling_end_time_stamp = time_stamp >> (64 - PAGE_THRASHING_THROTTLING_END_TIME_STAMP_BITS);
}

// Performance heuristics module for thrashing
static uvm_perf_module_t g_module_thrashing;

// Callback declaration for the performance heuristics events
static void thrashing_event_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data);
static void thrashing_block_destroy_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data);
static void thrashing_block_munmap_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data);

static uvm_perf_module_event_callback_desc_t g_callbacks_thrashing[] = {
    { UVM_PERF_EVENT_BLOCK_DESTROY, thrashing_block_destroy_cb },
    { UVM_PERF_EVENT_MODULE_UNLOAD, thrashing_block_destroy_cb },
    { UVM_PERF_EVENT_BLOCK_SHRINK , thrashing_block_destroy_cb },
    { UVM_PERF_EVENT_BLOCK_MUNMAP , thrashing_block_munmap_cb  },
    { UVM_PERF_EVENT_MIGRATION,     thrashing_event_cb         },
    { UVM_PERF_EVENT_REVOCATION,    thrashing_event_cb         }
};

static int nv_procfs_read_thrashing_stats(struct seq_file *s, void *v)
{
    processor_thrashing_stats_t *processor_stats = (processor_thrashing_stats_t *)s->private;

    UVM_ASSERT(processor_stats);

    if (!uvm_down_read_trylock(&g_uvm_global.pm.lock))
            return -EAGAIN;

    UVM_SEQ_OR_DBG_PRINT(s, "thrashing     %llu\n", (NvU64)atomic64_read(&processor_stats->num_thrashing));
    UVM_SEQ_OR_DBG_PRINT(s, "throttle      %llu\n", (NvU64)atomic64_read(&processor_stats->num_throttle));
    UVM_SEQ_OR_DBG_PRINT(s, "pin_local     %llu\n", (NvU64)atomic64_read(&processor_stats->num_pin_local));
    UVM_SEQ_OR_DBG_PRINT(s, "pin_remote    %llu\n", (NvU64)atomic64_read(&processor_stats->num_pin_remote));

    uvm_up_read(&g_uvm_global.pm.lock);

    return 0;
}

static int nv_procfs_read_thrashing_stats_entry(struct seq_file *s, void *v)
{
    UVM_ENTRY_RET(nv_procfs_read_thrashing_stats(s, v));
}

UVM_DEFINE_SINGLE_PROCFS_FILE(thrashing_stats_entry);

#define THRASHING_STATS_FILE_NAME "thrashing_stats"

// Initialization/deinitialization of CPU thrashing stats
//
static NV_STATUS cpu_thrashing_stats_init(void)
{
    struct proc_dir_entry *cpu_base_dir_entry = uvm_procfs_get_cpu_base_dir();

    if (uvm_procfs_is_debug_enabled()) {
        UVM_ASSERT(!g_cpu_thrashing_stats.procfs_file);
        g_cpu_thrashing_stats.procfs_file = NV_CREATE_PROC_FILE(THRASHING_STATS_FILE_NAME,
                                                                cpu_base_dir_entry,
                                                                thrashing_stats_entry,
                                                                &g_cpu_thrashing_stats);
        if (!g_cpu_thrashing_stats.procfs_file)
            return NV_ERR_OPERATING_SYSTEM;
    }

    return NV_OK;
}

static void cpu_thrashing_stats_exit(void)
{
    if (g_cpu_thrashing_stats.procfs_file) {
        UVM_ASSERT(uvm_procfs_is_debug_enabled());
        proc_remove(g_cpu_thrashing_stats.procfs_file);
        g_cpu_thrashing_stats.procfs_file = NULL;
    }
}

// Get the thrashing stats struct for the given VA space if it exists
//
// No lock may be held. Therefore, the stats must be updated using atomics
static processor_thrashing_stats_t *gpu_thrashing_stats_get_or_null(uvm_gpu_t *gpu)
{
    return uvm_perf_module_type_data(gpu->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);
}

static processor_thrashing_stats_t *thrashing_stats_get_or_null(uvm_va_space_t *va_space, uvm_processor_id_t id)
{
    if (UVM_ID_IS_CPU(id)) {
        if (g_cpu_thrashing_stats.procfs_file)
            return &g_cpu_thrashing_stats;

        return NULL;
    }

    return gpu_thrashing_stats_get_or_null(uvm_va_space_get_gpu(va_space, id));
}

// Create the thrashing stats struct for the given GPU
//
// Global lock needs to be held
static NV_STATUS gpu_thrashing_stats_create(uvm_gpu_t *gpu)
{
    processor_thrashing_stats_t *gpu_thrashing;

    uvm_assert_mutex_locked(&g_uvm_global.global_lock);
    UVM_ASSERT(gpu_thrashing_stats_get_or_null(gpu) == NULL);
    UVM_ASSERT(uvm_procfs_is_debug_enabled());

    gpu_thrashing = uvm_kvmalloc_zero(sizeof(*gpu_thrashing));
    if (!gpu_thrashing)
        return NV_ERR_NO_MEMORY;

    gpu_thrashing->procfs_file = NV_CREATE_PROC_FILE(THRASHING_STATS_FILE_NAME,
                                                     gpu->procfs.dir,
                                                     thrashing_stats_entry,
                                                     gpu_thrashing);
    if (!gpu_thrashing->procfs_file) {
        uvm_kvfree(gpu_thrashing);
        return NV_ERR_OPERATING_SYSTEM;
    }

    uvm_perf_module_type_set_data(gpu->perf_modules_data, gpu_thrashing, UVM_PERF_MODULE_TYPE_THRASHING);

    return NV_OK;
}

static void gpu_thrashing_stats_destroy(uvm_gpu_t *gpu)
{
    processor_thrashing_stats_t *gpu_thrashing = gpu_thrashing_stats_get_or_null(gpu);

    uvm_assert_mutex_locked(&g_uvm_global.global_lock);

    if (gpu_thrashing) {
        uvm_perf_module_type_unset_data(gpu->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);

        if (gpu_thrashing->procfs_file)
            proc_remove(gpu_thrashing->procfs_file);

        uvm_kvfree(gpu_thrashing);
    }
}

// Get the thrashing detection struct for the given VA space if it exists
//
// The caller must ensure that the va_space cannot be deleted, for the
// duration of this call. Holding either the va_block or va_space lock will do
// that.
static va_space_thrashing_info_t *va_space_thrashing_info_get_or_null(uvm_va_space_t *va_space)
{
    return uvm_perf_module_type_data(va_space->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);
}

// Get the thrashing detection struct for the given VA space. It asserts that
// the information has been previously created.
//
// The caller must ensure that the va_space cannot be deleted, for the
// duration of this call. Holding either the va_block or va_space lock will do
// that.
static va_space_thrashing_info_t *va_space_thrashing_info_get(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get_or_null(va_space);
    UVM_ASSERT(va_space_thrashing);

    return va_space_thrashing;
}

static void va_space_thrashing_info_init_params(va_space_thrashing_info_t *va_space_thrashing)
{
    UVM_ASSERT(!va_space_thrashing->params.test_overrides);

    va_space_thrashing->params.enable = g_uvm_perf_thrashing_enable;

    // Snap the thrashing parameters so that they can be tuned per VA space
    va_space_thrashing->params.threshold     = g_uvm_perf_thrashing_threshold;
    va_space_thrashing->params.pin_threshold = g_uvm_perf_thrashing_pin_threshold;

    // Default thrashing parameters are overriden for simulated/emulated GPUs
    if (g_uvm_global.num_simulated_devices > 0 &&
        (g_uvm_perf_thrashing_lapse_usec == UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT)) {
        va_space_thrashing->params.lapse_ns  = UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT_EMULATION * 1000;
    }
    else {
        va_space_thrashing->params.lapse_ns  = g_uvm_perf_thrashing_lapse_usec * 1000;
    }

    va_space_thrashing->params.nap_ns        = va_space_thrashing->params.lapse_ns * g_uvm_perf_thrashing_nap;
    va_space_thrashing->params.epoch_ns      = va_space_thrashing->params.lapse_ns * g_uvm_perf_thrashing_epoch;

    if (g_uvm_global.num_simulated_devices > 0 && (g_uvm_perf_thrashing_pin == UVM_PERF_THRASHING_PIN_DEFAULT)) {
        va_space_thrashing->params.pin_ns    = va_space_thrashing->params.lapse_ns
                                               * UVM_PERF_THRASHING_PIN_DEFAULT_EMULATION;
    }
    else {
        va_space_thrashing->params.pin_ns    = va_space_thrashing->params.lapse_ns * g_uvm_perf_thrashing_pin;
    }

    va_space_thrashing->params.max_resets    = g_uvm_perf_thrashing_max_resets;
}

// Create the thrashing detection struct for the given VA space
//
// VA space lock needs to be held in write mode
static va_space_thrashing_info_t *va_space_thrashing_info_create(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing;
    uvm_assert_rwsem_locked_write(&va_space->lock);

    UVM_ASSERT(va_space_thrashing_info_get_or_null(va_space) == NULL);

    va_space_thrashing = uvm_kvmalloc_zero(sizeof(*va_space_thrashing));
    if (va_space_thrashing) {
        uvm_va_block_context_t *block_context = uvm_va_block_context_alloc(NULL);

        if (!block_context) {
            uvm_kvfree(va_space_thrashing);
            return NULL;
        }

        va_space_thrashing->pinned_pages.va_block_context = block_context;
        va_space_thrashing->va_space = va_space;

        va_space_thrashing_info_init_params(va_space_thrashing);

        uvm_perf_module_type_set_data(va_space->perf_modules_data, va_space_thrashing, UVM_PERF_MODULE_TYPE_THRASHING);
    }

    return va_space_thrashing;
}

// Destroy the thrashing detection struct for the given VA space
//
// VA space lock needs to be in write mode
static void va_space_thrashing_info_destroy(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get_or_null(va_space);
    uvm_assert_rwsem_locked_write(&va_space->lock);

    if (va_space_thrashing) {
        uvm_perf_module_type_unset_data(va_space->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);
        uvm_va_block_context_free(va_space_thrashing->pinned_pages.va_block_context);
        uvm_kvfree(va_space_thrashing);
    }
}

// Get the thrashing detection struct for the given block
static block_thrashing_info_t *thrashing_info_get(uvm_va_block_t *va_block)
{
    uvm_assert_mutex_locked(&va_block->lock);
    return uvm_perf_module_type_data(va_block->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);
}

// Get the thrashing detection struct for the given block or create it if it
// does not exist
static block_thrashing_info_t *thrashing_info_get_create(uvm_va_block_t *va_block)
{
    block_thrashing_info_t *block_thrashing = thrashing_info_get(va_block);

    BUILD_BUG_ON((1 << 8 * sizeof(block_thrashing->num_thrashing_pages)) < PAGES_PER_UVM_VA_BLOCK);
    BUILD_BUG_ON((1 << 16) < UVM_ID_MAX_PROCESSORS);

    if (!block_thrashing) {
        block_thrashing = nv_kmem_cache_zalloc(g_va_block_thrashing_info_cache, NV_UVM_GFP_FLAGS);
        if (!block_thrashing)
            goto done;

        block_thrashing->last_processor = UVM_ID_INVALID;
        INIT_LIST_HEAD(&block_thrashing->pinned_pages.list);

        uvm_perf_module_type_set_data(va_block->perf_modules_data, block_thrashing, UVM_PERF_MODULE_TYPE_THRASHING);
    }

done:
    return block_thrashing;
}

static void thrashing_reset_pages_in_region(uvm_va_block_t *va_block, NvU64 address, NvU64 bytes);

void uvm_perf_thrashing_info_destroy(uvm_va_block_t *va_block)
{
    block_thrashing_info_t *block_thrashing = thrashing_info_get(va_block);

    if (block_thrashing) {
        thrashing_reset_pages_in_region(va_block, va_block->start, uvm_va_block_size(va_block));

        uvm_perf_module_type_unset_data(va_block->perf_modules_data, UVM_PERF_MODULE_TYPE_THRASHING);

        uvm_kvfree(block_thrashing->pages);
        kmem_cache_free(g_va_block_thrashing_info_cache, block_thrashing);
    }
}

void thrashing_block_destroy_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data)
{
    uvm_va_block_t *va_block;

    UVM_ASSERT(g_uvm_perf_thrashing_enable);

    UVM_ASSERT(event_id == UVM_PERF_EVENT_BLOCK_DESTROY ||
               event_id == UVM_PERF_EVENT_BLOCK_SHRINK ||
               event_id == UVM_PERF_EVENT_MODULE_UNLOAD);

    if (event_id == UVM_PERF_EVENT_BLOCK_DESTROY)
        va_block = event_data->block_destroy.block;
    else if (event_id == UVM_PERF_EVENT_BLOCK_SHRINK)
        va_block = event_data->block_shrink.block;
    else
        va_block = event_data->module_unload.block;

    if (!va_block)
        return;

    uvm_perf_thrashing_info_destroy(va_block);
}

void thrashing_block_munmap_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data)
{
    uvm_va_block_t *va_block = event_data->block_munmap.block;
    uvm_va_block_region_t region = event_data->block_munmap.region;

    UVM_ASSERT(g_uvm_perf_thrashing_enable);
    UVM_ASSERT(event_id == UVM_PERF_EVENT_BLOCK_MUNMAP);
    UVM_ASSERT(va_block);

    thrashing_reset_pages_in_region(va_block,
                                    uvm_va_block_region_start(va_block, region),
                                    uvm_va_block_region_size(region));
}

// Sanity checks of the thrashing tracking state
static bool thrashing_state_checks(uvm_va_block_t *va_block,
                                   block_thrashing_info_t *block_thrashing,
                                   page_thrashing_info_t *page_thrashing,
                                   uvm_page_index_t page_index)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);

    if (!block_thrashing) {
        UVM_ASSERT(!page_thrashing);
        return true;
    }

    UVM_ASSERT(uvm_page_mask_subset(&block_thrashing->pinned_pages.mask, &block_thrashing->thrashing_pages));

    if (page_thrashing) {
        UVM_ASSERT(block_thrashing->pages);
        UVM_ASSERT(page_thrashing == &block_thrashing->pages[page_index]);
    }
    else {
        UVM_ASSERT(!uvm_page_mask_test(&block_thrashing->thrashing_pages, page_index));
        return true;
    }

    UVM_ASSERT(uvm_processor_mask_subset(&page_thrashing->throttled_processors,
                                         &page_thrashing->processors));

    if (uvm_page_mask_test(&block_thrashing->thrashing_pages, page_index))
        UVM_ASSERT(page_thrashing->num_thrashing_events >= va_space_thrashing->params.threshold);

    if (page_thrashing->pinned) {
        UVM_ASSERT(uvm_page_mask_test(&block_thrashing->pinned_pages.mask, page_index));
        UVM_ASSERT(UVM_ID_IS_VALID(page_thrashing->pinned_residency_id));
        UVM_ASSERT(page_thrashing->throttling_count == 0);
    }
    else {
        UVM_ASSERT(!uvm_page_mask_test(&block_thrashing->pinned_pages.mask, page_index));
        UVM_ASSERT(UVM_ID_IS_INVALID(page_thrashing->pinned_residency_id));

        if (!uvm_processor_mask_empty(&page_thrashing->throttled_processors)) {
            UVM_ASSERT(page_thrashing->throttling_count > 0);
            UVM_ASSERT(uvm_page_mask_test(&block_thrashing->thrashing_pages, page_index));
        }
    }

    return true;
}

// Update throttling heuristics. Mainly check if a new throttling period has
// started and choose the next processor not to be throttled. This function
// is executed before the thrashing mitigation logic kicks in.
static void thrashing_throttle_update(va_space_thrashing_info_t *va_space_thrashing,
                                      uvm_va_block_t *va_block,
                                      page_thrashing_info_t *page_thrashing,
                                      uvm_processor_id_t processor,
                                      NvU64 time_stamp)
{
    NvU64 current_end_time_stamp = page_thrashing_get_throttling_end_time_stamp(page_thrashing);

    uvm_assert_mutex_locked(&va_block->lock);

    if (time_stamp > current_end_time_stamp) {
        NvU64 throttling_end_time_stamp = time_stamp + va_space_thrashing->params.nap_ns;
        page_thrashing_set_throttling_end_time_stamp(page_thrashing, throttling_end_time_stamp);

        // Avoid choosing the same processor in consecutive thrashing periods
        if (uvm_id_equal(page_thrashing->do_not_throttle_processor_id, processor))
            page_thrashing->do_not_throttle_processor_id = UVM_ID_INVALID;
        else
            page_thrashing->do_not_throttle_processor_id = processor;
    }
    else if (UVM_ID_IS_INVALID(page_thrashing->do_not_throttle_processor_id)) {
        page_thrashing->do_not_throttle_processor_id = processor;
    }
}

// Throttle the execution of a processor. If this is the first processor being
// throttled for a throttling period, compute the time stamp until which the
// rest of processors will be throttled on fault.
//
// - Page may be pinned (possible in thrashing due to revocation, such as
//   in system-wide atomics)
// - Requesting processor must not be throttled at this point.
//
static void thrashing_throttle_processor(uvm_va_block_t *va_block,
                                         block_thrashing_info_t *block_thrashing,
                                         page_thrashing_info_t *page_thrashing,
                                         uvm_page_index_t page_index,
                                         uvm_processor_id_t processor)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    NvU64 address = uvm_va_block_cpu_page_address(va_block, page_index);

    uvm_assert_mutex_locked(&va_block->lock);

    UVM_ASSERT(!uvm_id_equal(processor, page_thrashing->do_not_throttle_processor_id));

    if (!uvm_processor_mask_test_and_set(&page_thrashing->throttled_processors, processor)) {
        // CPU is throttled by sleeping. This is done in uvm_vm_fault so it
        // drops the VA block and VA space locks. Throttling start/end events
        // are recorded around the sleep calls.
        if (UVM_ID_IS_GPU(processor))
            uvm_tools_record_throttling_start(va_space, address, processor);

        if (!page_thrashing->pinned)
            UVM_PERF_SATURATING_INC(page_thrashing->throttling_count);

        UVM_PERF_SATURATING_INC(block_thrashing->throttling_count);
    }

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));
}

// Stop throttling on the given processor. If this is the last processor being
// throttled for a throttling period, it will clear the throttling period.
//
// - Page may be pinned (possible in thrashing due to revocation, such as
//   in system-wide atomics)
// - Requesting processor must be throttled at this point.
//
static void thrashing_throttle_end_processor(uvm_va_block_t *va_block,
                                             block_thrashing_info_t *block_thrashing,
                                             page_thrashing_info_t *page_thrashing,
                                             uvm_page_index_t page_index,
                                             uvm_processor_id_t processor)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    NvU64 address = uvm_va_block_cpu_page_address(va_block, page_index);

    UVM_ASSERT(uvm_processor_mask_test(&page_thrashing->throttled_processors, processor));
    uvm_processor_mask_clear(&page_thrashing->throttled_processors, processor);
    if (uvm_processor_mask_empty(&page_thrashing->throttled_processors))
        page_thrashing_set_throttling_end_time_stamp(page_thrashing, 0);

    // See comment regarding throttling start/end events for CPU in
    // thrashing_throttle_processor
    if (UVM_ID_IS_GPU(processor))
        uvm_tools_record_throttling_end(va_space, address, processor);

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));
}

// Clear the throttling state for all processors. This is used while
// transitioning to pinned state and during thrashing information reset.
static void thrashing_throttling_reset_page(uvm_va_block_t *va_block,
                                            block_thrashing_info_t *block_thrashing,
                                            page_thrashing_info_t *page_thrashing,
                                            uvm_page_index_t page_index)
{
    uvm_processor_id_t processor_id;

    for_each_id_in_mask(processor_id, &page_thrashing->throttled_processors) {
        thrashing_throttle_end_processor(va_block,
                                         block_thrashing,
                                         page_thrashing,
                                         page_index,
                                         processor_id);
    }

    UVM_ASSERT(uvm_processor_mask_empty(&page_thrashing->throttled_processors));
}

// Find the pinned page descriptor for the given page index. Return NULL if the
// page is not pinned.
static pinned_page_t *find_pinned_page(block_thrashing_info_t *block_thrashing, uvm_page_index_t page_index)
{
    pinned_page_t *pinned_page;

    list_for_each_entry(pinned_page, &block_thrashing->pinned_pages.list, va_block_list_entry) {
        if (pinned_page->page_index == page_index)
            return pinned_page;
    }

    return NULL;
}

// Pin a page on the specified processor. All thrashing processors will be
// mapped remotely on this location, when possible
//
// - Requesting processor cannot be throttled
//
static NV_STATUS thrashing_pin_page(va_space_thrashing_info_t *va_space_thrashing,
                                    uvm_va_block_t *va_block,
                                    block_thrashing_info_t *block_thrashing,
                                    page_thrashing_info_t *page_thrashing,
                                    uvm_page_index_t page_index,
                                    NvU64 time_stamp,
                                    uvm_processor_id_t residency,
                                    uvm_processor_id_t requester)
{
    uvm_processor_mask_t current_residency;

    uvm_assert_mutex_locked(&va_block->lock);
    UVM_ASSERT(!uvm_processor_mask_test(&page_thrashing->throttled_processors, requester));

    uvm_va_block_page_resident_processors(va_block, page_index, &current_residency);

    // If we are pinning the page for the first time or we are pinning it on a
    // different location that the current location, reset the throttling state
    // to make sure that we flush any pending ThrottlingEnd events.
    if (!page_thrashing->pinned || !uvm_processor_mask_test(&current_residency, residency))
        thrashing_throttling_reset_page(va_block, block_thrashing, page_thrashing, page_index);

    if (!page_thrashing->pinned) {
        if (va_space_thrashing->params.pin_ns > 0) {
            pinned_page_t *pinned_page = nv_kmem_cache_zalloc(g_pinned_page_cache, NV_UVM_GFP_FLAGS);
            if (!pinned_page)
                return NV_ERR_NO_MEMORY;

            pinned_page->va_block = va_block;
            pinned_page->page_index = page_index;
            pinned_page->deadline = time_stamp + va_space_thrashing->params.pin_ns;

            uvm_spin_lock(&va_space_thrashing->pinned_pages.lock);

            list_add_tail(&pinned_page->va_space_list_entry, &va_space_thrashing->pinned_pages.list);
            list_add_tail(&pinned_page->va_block_list_entry, &block_thrashing->pinned_pages.list);

            // We only schedule the delayed work if the list was empty before
            // adding this page. Otherwise, we just add it to the list. The
            // unpinning helper will remove from the list those pages with
            // deadline prior to its wakeup timestamp and will reschedule
            // itself if there are remaining pages in the list.
            if (list_is_singular(&va_space_thrashing->pinned_pages.list) &&
                !va_space_thrashing->pinned_pages.in_va_space_teardown) {
                int scheduled;
                scheduled = schedule_delayed_work(&va_space_thrashing->pinned_pages.dwork,
                                                  usecs_to_jiffies(va_space_thrashing->params.pin_ns / 1000));
                UVM_ASSERT(scheduled != 0);
            }

            uvm_spin_unlock(&va_space_thrashing->pinned_pages.lock);
        }

        page_thrashing->throttling_count = 0;
        page_thrashing->pinned = true;
        UVM_PERF_SATURATING_INC(block_thrashing->pinned_pages.count);
        uvm_page_mask_set(&block_thrashing->pinned_pages.mask, page_index);
    }

    page_thrashing->pinned_residency_id = residency;

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));

    return NV_OK;
}

// Unpin a page. This function just clears the pinning tracking state, and does
// not remove remote mappings on the page. Callers will need to do it manually
// BEFORE calling this function, if so desired.
// - Page must be pinned
//
static void thrashing_unpin_page(va_space_thrashing_info_t *va_space_thrashing,
                                 uvm_va_block_t *va_block,
                                 block_thrashing_info_t *block_thrashing,
                                 page_thrashing_info_t *page_thrashing,
                                 uvm_page_index_t page_index)
{
    uvm_assert_mutex_locked(&va_block->lock);
    UVM_ASSERT(page_thrashing->pinned);

    if (va_space_thrashing->params.pin_ns > 0) {
        bool do_free = false;
        pinned_page_t *pinned_page = find_pinned_page(block_thrashing, page_index);

        UVM_ASSERT(pinned_page);
        UVM_ASSERT(pinned_page->page_index == page_index);
        UVM_ASSERT(pinned_page->va_block == va_block);

        // The va_space_list_entry and va_block_list_entry have special
        // meanings here:
        // - va_space_list_entry: when the delayed unpin worker removes the
        // pinned_page from this list, it takes the ownership of the page and
        // is in charge of freeing it.
        // - va_block_list_entry: by removing the page from this list,
        // thrashing_unpin_page tells the unpin delayed worker to skip
        // unpinning that page.
        uvm_spin_lock(&va_space_thrashing->pinned_pages.lock);
        list_del_init(&pinned_page->va_block_list_entry);

        if (!list_empty(&pinned_page->va_space_list_entry)) {
            do_free = true;
            list_del_init(&pinned_page->va_space_list_entry);

            if (list_empty(&va_space_thrashing->pinned_pages.list))
                cancel_delayed_work(&va_space_thrashing->pinned_pages.dwork);
        }

        uvm_spin_unlock(&va_space_thrashing->pinned_pages.lock);

        if (do_free)
            kmem_cache_free(g_pinned_page_cache, pinned_page);
    }

    page_thrashing->pinned_residency_id = UVM_ID_INVALID;
    page_thrashing->pinned = false;
    uvm_page_mask_clear(&block_thrashing->pinned_pages.mask, page_index);

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));
}

static void thrashing_detected(uvm_va_block_t *va_block,
                               block_thrashing_info_t *block_thrashing,
                               page_thrashing_info_t *page_thrashing,
                               uvm_page_index_t page_index,
                               uvm_processor_id_t processor_id)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    NvU64 address = uvm_va_block_cpu_page_address(va_block, page_index);

    // Thrashing detected, record the event
    uvm_tools_record_thrashing(va_space, address, PAGE_SIZE, &page_thrashing->processors);
    if (!uvm_page_mask_test_and_set(&block_thrashing->thrashing_pages, page_index))
        ++block_thrashing->num_thrashing_pages;

    PROCESSOR_THRASHING_STATS_INC(va_space, processor_id, num_thrashing);

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));
}

// Clear the thrashing information for the given page. This function does not
// unmap remote mappings on the page. Callers will need to do it BEFORE calling
// this function, if so desired
static void thrashing_reset_page(va_space_thrashing_info_t *va_space_thrashing,
                                 uvm_va_block_t *va_block,
                                 block_thrashing_info_t *block_thrashing,
                                 uvm_page_index_t page_index)
{
    page_thrashing_info_t *page_thrashing = &block_thrashing->pages[page_index];
    uvm_assert_mutex_locked(&va_block->lock);

    UVM_ASSERT(block_thrashing->num_thrashing_pages > 0);
    UVM_ASSERT(uvm_page_mask_test(&block_thrashing->thrashing_pages, page_index));
    UVM_ASSERT(page_thrashing->num_thrashing_events > 0);

    thrashing_throttling_reset_page(va_block, block_thrashing, page_thrashing, page_index);
    UVM_ASSERT(uvm_processor_mask_empty(&page_thrashing->throttled_processors));

    if (page_thrashing->pinned)
        thrashing_unpin_page(va_space_thrashing, va_block, block_thrashing, page_thrashing, page_index);

    page_thrashing->last_time_stamp       = 0;
    page_thrashing->has_migration_events  = 0;
    page_thrashing->has_revocation_events = 0;
    page_thrashing->num_thrashing_events  = 0;
    uvm_processor_mask_zero(&page_thrashing->processors);

    if (uvm_page_mask_test_and_clear(&block_thrashing->thrashing_pages, page_index))
        --block_thrashing->num_thrashing_pages;

    UVM_ASSERT(thrashing_state_checks(va_block, block_thrashing, page_thrashing, page_index));
}

// Call thrashing_reset_page for all the thrashing pages in the region
// described by address and bytes
static void thrashing_reset_pages_in_region(uvm_va_block_t *va_block, NvU64 address, NvU64 bytes)
{
    uvm_page_index_t page_index;
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);
    block_thrashing_info_t *block_thrashing = NULL;
    uvm_va_block_region_t region = uvm_va_block_region_from_start_size(va_block, address, bytes);

    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing || !block_thrashing->pages)
        return;

    // Update all pages in the region
    for_each_va_block_page_in_region_mask(page_index, &block_thrashing->thrashing_pages, region)
        thrashing_reset_page(va_space_thrashing, va_block, block_thrashing, page_index);
}


// Unmap remote mappings from the given processors on the pinned pages
// described by region and block_thrashing->pinned pages.
static NV_STATUS unmap_remote_pinned_pages(uvm_va_block_t *va_block,
                                           uvm_va_block_context_t *va_block_context,
                                           block_thrashing_info_t *block_thrashing,
                                           uvm_va_block_region_t region,
                                           const uvm_processor_mask_t *unmap_processors)
{
    NV_STATUS status = NV_OK;
    NV_STATUS tracker_status;
    uvm_tracker_t local_tracker = UVM_TRACKER_INIT();
    uvm_processor_id_t processor_id;
    const uvm_va_policy_t *policy = uvm_va_policy_get(va_block, uvm_va_block_region_start(va_block, region));

    uvm_assert_mutex_locked(&va_block->lock);

    for_each_id_in_mask(processor_id, unmap_processors) {
        UVM_ASSERT(uvm_id_equal(processor_id, policy->preferred_location) ||
                   !uvm_processor_mask_test(&policy->accessed_by, processor_id));

        if (uvm_processor_mask_test(&va_block->resident, processor_id)) {
            const uvm_page_mask_t *resident_mask = uvm_va_block_resident_mask_get(va_block, processor_id, NUMA_NO_NODE);

            if (!uvm_page_mask_andnot(&va_block_context->caller_page_mask,
                                      &block_thrashing->pinned_pages.mask,
                                      resident_mask))
                continue;
        }
        else {
            uvm_page_mask_copy(&va_block_context->caller_page_mask,
                               &block_thrashing->pinned_pages.mask);
        }

        status = uvm_va_block_unmap(va_block,
                                    va_block_context,
                                    processor_id,
                                    region,
                                    &va_block_context->caller_page_mask,
                                    &local_tracker);
        if (status != NV_OK)
            break;
    }

    tracker_status = uvm_tracker_add_tracker_safe(&va_block->tracker, &local_tracker);
    if (status == NV_OK)
        status = tracker_status;

    uvm_tracker_deinit(&local_tracker);

    return status;
}

NV_STATUS uvm_perf_thrashing_unmap_remote_pinned_pages_all(uvm_va_block_t *va_block,
                                                           uvm_va_block_context_t *va_block_context,
                                                           uvm_va_block_region_t region)
{
    block_thrashing_info_t *block_thrashing;
    uvm_processor_mask_t unmap_processors;
    const uvm_va_policy_t *policy = uvm_va_policy_get_region(va_block, region);

    uvm_assert_mutex_locked(&va_block->lock);

    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing || !block_thrashing->pages)
        return NV_OK;

    if (uvm_page_mask_empty(&block_thrashing->pinned_pages.mask))
        return NV_OK;

    // Unmap all mapped processors (that are not SetAccessedBy) with
    // no copy of the page
    uvm_processor_mask_andnot(&unmap_processors, &va_block->mapped, &policy->accessed_by);

    return unmap_remote_pinned_pages(va_block, va_block_context, block_thrashing, region, &unmap_processors);
}

// Check that we are not migrating pages away from its pinned location and
// that we are not prefetching thrashing pages.
static bool migrating_wrong_pages(uvm_va_block_t *va_block,
                                  NvU64 address,
                                  NvU64 bytes,
                                  uvm_processor_id_t proc_id,
                                  uvm_make_resident_cause_t cause)
{
    uvm_page_index_t page_index;
    block_thrashing_info_t *block_thrashing = NULL;
    uvm_va_block_region_t region = uvm_va_block_region_from_start_size(va_block, address, bytes);

    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing || !block_thrashing->pages)
        return false;

    for_each_va_block_page_in_region(page_index, region) {
        page_thrashing_info_t *page_thrashing = &block_thrashing->pages[page_index];
        UVM_ASSERT_MSG(!page_thrashing->pinned || uvm_id_equal(proc_id, page_thrashing->pinned_residency_id),
                       "Migrating to %u instead of %u\n",
                       uvm_id_value(proc_id), uvm_id_value(page_thrashing->pinned_residency_id));
        if (cause == UVM_MAKE_RESIDENT_CAUSE_PREFETCH)
            UVM_ASSERT(!uvm_page_mask_test(&block_thrashing->thrashing_pages, page_index));
    }

    return false;
}

static bool is_migration_pinned_pages_update(uvm_va_block_t *va_block,
                                             const uvm_perf_event_data_t *event_data,
                                             NvU64 address,
                                             NvU64 bytes)
{
    const block_thrashing_info_t *block_thrashing = NULL;
    uvm_va_block_region_t region = uvm_va_block_region_from_start_size(va_block, address, bytes);
    bool ret;

    if (event_data->migration.cause != UVM_MAKE_RESIDENT_CAUSE_REPLAYABLE_FAULT &&
        event_data->migration.cause != UVM_MAKE_RESIDENT_CAUSE_ACCESS_COUNTER) {
        return false;
    }

    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing || !block_thrashing->pages)
        return false;

    ret = uvm_page_mask_region_full(&block_thrashing->pinned_pages.mask, region);
    if (ret) {
        uvm_page_index_t page_index;
        for_each_va_block_page_in_region(page_index, region) {
            page_thrashing_info_t *page_thrashing = &block_thrashing->pages[page_index];
            UVM_ASSERT(uvm_id_equal(page_thrashing->pinned_residency_id, event_data->migration.dst));
        }
    }

    return ret;
}

// This function processes migration/revocation events and determines if the
// affected pages are thrashing or not.
void thrashing_event_cb(uvm_perf_event_t event_id, uvm_perf_event_data_t *event_data)
{
    va_space_thrashing_info_t *va_space_thrashing;
    block_thrashing_info_t *block_thrashing = NULL;
    uvm_va_block_t *va_block;
    uvm_va_space_t *va_space;
    NvU64 address;
    NvU64 bytes;
    uvm_processor_id_t processor_id;
    uvm_page_index_t page_index;
    NvU64 time_stamp;
    uvm_va_block_region_t region;
    uvm_read_duplication_policy_t read_duplication;

    UVM_ASSERT(g_uvm_perf_thrashing_enable);

    UVM_ASSERT(event_id == UVM_PERF_EVENT_MIGRATION || event_id == UVM_PERF_EVENT_REVOCATION);

    if (event_id == UVM_PERF_EVENT_MIGRATION) {
        va_block     = event_data->migration.block;
        address      = event_data->migration.address;
        bytes        = event_data->migration.bytes;
        processor_id = event_data->migration.dst;

        // Skip the thrashing detection logic on eviction as we cannot take
        // the VA space lock
        if (event_data->migration.cause == UVM_MAKE_RESIDENT_CAUSE_EVICTION)
            return;

        // Do not perform checks during the first part of staging copies
        if (!uvm_id_equal(event_data->migration.dst, event_data->migration.make_resident_context->dest_id))
            return;

        va_space = uvm_va_block_get_va_space(va_block);
        va_space_thrashing = va_space_thrashing_info_get(va_space);
        if (!va_space_thrashing->params.enable)
            return;

        // TODO: Bug 3660922: HMM will need to look up the policy when
        // read duplication is supported.
        read_duplication = uvm_va_block_is_hmm(va_block) ?
                           UVM_READ_DUPLICATION_UNSET :
                           uvm_va_range_get_policy(va_block->va_range)->read_duplication;

        // We only care about migrations due to replayable faults, access
        // counters and page prefetching. For non-replayable faults, UVM will
        // try not to migrate memory since CE is transferring data anyway.
        // However, we can still see migration events due to initial
        // population. The rest of migrations are triggered due to user
        // commands or advice (such as read duplication) which takes precedence
        // over our heuristics. Therefore, we clear our internal tracking
        // state.
        if ((event_data->migration.cause != UVM_MAKE_RESIDENT_CAUSE_REPLAYABLE_FAULT &&
             event_data->migration.cause != UVM_MAKE_RESIDENT_CAUSE_ACCESS_COUNTER &&
             event_data->migration.cause != UVM_MAKE_RESIDENT_CAUSE_PREFETCH) ||
            (event_data->migration.transfer_mode != UVM_VA_BLOCK_TRANSFER_MODE_MOVE) ||
            (read_duplication == UVM_READ_DUPLICATION_ENABLED)) {
            thrashing_reset_pages_in_region(va_block, address, bytes);
            return;
        }

        // Assert that we are not migrating pages that are pinned away from
        // their pinning residency, or prefetching pages that are thrashing
        UVM_ASSERT(!migrating_wrong_pages(va_block, address, bytes, processor_id, event_data->migration.cause));

        // If we are being migrated due to pinning just return
        if (is_migration_pinned_pages_update(va_block, event_data, address, bytes))
            return;
    }
    else {
        va_block     = event_data->revocation.block;
        address      = event_data->revocation.address;
        bytes        = event_data->revocation.bytes;
        processor_id = event_data->revocation.proc_id;

        va_space = uvm_va_block_get_va_space(va_block);
        va_space_thrashing = va_space_thrashing_info_get(va_space);
        if (!va_space_thrashing->params.enable)
            return;
    }

    block_thrashing = thrashing_info_get_create(va_block);
    if (!block_thrashing)
        return;

    time_stamp = NV_GETTIME();

    if (!block_thrashing->pages) {
        // Don't create the per-page tracking structure unless there is some potential thrashing within the block
        NvU16 num_block_pages;

        if (block_thrashing->last_time_stamp == 0 ||
            uvm_id_equal(block_thrashing->last_processor, processor_id) ||
            time_stamp - block_thrashing->last_time_stamp > va_space_thrashing->params.lapse_ns)
            goto done;

        num_block_pages = uvm_va_block_size(va_block) / PAGE_SIZE;

        block_thrashing->pages = uvm_kvmalloc_zero(sizeof(*block_thrashing->pages) * num_block_pages);
        if (!block_thrashing->pages)
            goto done;

        for (page_index = 0; page_index < num_block_pages; ++page_index) {
            block_thrashing->pages[page_index].pinned_residency_id = UVM_ID_INVALID;
            block_thrashing->pages[page_index].do_not_throttle_processor_id = UVM_ID_INVALID;
        }
    }

    region = uvm_va_block_region_from_start_size(va_block, address, bytes);

    // Update all pages in the region
    for_each_va_block_page_in_region(page_index, region) {
        page_thrashing_info_t *page_thrashing = &block_thrashing->pages[page_index];
        NvU64 last_time_stamp = page_thrashing_get_time_stamp(page_thrashing);

        // It is not possible that a pinned page is migrated here, since the
        // fault that triggered the migration should have unpinned it in its
        // call to uvm_perf_thrashing_get_hint. Moreover page prefetching never
        // includes pages that are thrashing (including pinning)
        if (event_id == UVM_PERF_EVENT_MIGRATION)
            UVM_ASSERT(page_thrashing->pinned == 0);

        uvm_processor_mask_set(&page_thrashing->processors, processor_id);
        page_thrashing_set_time_stamp(page_thrashing, time_stamp);

        if (last_time_stamp == 0)
            continue;

        if (time_stamp - last_time_stamp <= va_space_thrashing->params.lapse_ns) {
            UVM_PERF_SATURATING_INC(page_thrashing->num_thrashing_events);
            if (page_thrashing->num_thrashing_events == va_space_thrashing->params.threshold)
                thrashing_detected(va_block, block_thrashing, page_thrashing, page_index, processor_id);

            if (page_thrashing->num_thrashing_events >= va_space_thrashing->params.threshold)
                block_thrashing->last_thrashing_time_stamp = time_stamp;

            if (event_id == UVM_PERF_EVENT_MIGRATION)
                page_thrashing->has_migration_events = true;
            else
                page_thrashing->has_revocation_events = true;
        }
        else if (page_thrashing->num_thrashing_events >= va_space_thrashing->params.threshold &&
                 !page_thrashing->pinned) {
            thrashing_reset_page(va_space_thrashing, va_block, block_thrashing, page_index);
        }
    }

done:
    block_thrashing->last_time_stamp = time_stamp;
    block_thrashing->last_processor  = processor_id;
}

static bool thrashing_processors_can_access(uvm_va_space_t *va_space,
                                            page_thrashing_info_t *page_thrashing,
                                            uvm_processor_id_t to)
{
    if (UVM_ID_IS_INVALID(to))
        return false;

    return uvm_processor_mask_subset(&page_thrashing->processors,
                                     &va_space->accessible_from[uvm_id_value(to)]);
}

static bool thrashing_processors_have_fast_access_to(uvm_va_space_t *va_space,
                                                     page_thrashing_info_t *page_thrashing,
                                                     uvm_processor_id_t to)
{
    uvm_processor_mask_t fast_to;

    if (UVM_ID_IS_INVALID(to))
        return false;

    // Combine NVLINK and native atomics mask since we could have PCIe
    // atomics in the future
    uvm_processor_mask_and(&fast_to,
                           &va_space->has_nvlink[uvm_id_value(to)],
                           &va_space->has_native_atomics[uvm_id_value(to)]);
    uvm_processor_mask_set(&fast_to, to);

    return uvm_processor_mask_subset(&page_thrashing->processors, &fast_to);
}

static void thrashing_processors_common_locations(uvm_va_space_t *va_space,
                                                  page_thrashing_info_t *page_thrashing,
                                                  uvm_processor_mask_t *common_locations)
{
    bool is_first = true;
    uvm_processor_id_t id;

    // Find processors that can be accessed from all thrashing processors. For
    // example: if A, B and C are thrashing, and A can access B and C can access
    // B, too, B would be the common location.
    uvm_processor_mask_zero(common_locations);

    for_each_id_in_mask(id, &page_thrashing->processors) {
        if (is_first)
            uvm_processor_mask_copy(common_locations, &va_space->can_access[uvm_id_value(id)]);
        else
            uvm_processor_mask_and(common_locations, common_locations, &va_space->can_access[uvm_id_value(id)]);

        is_first = false;
    }
}

static bool preferred_location_is_thrashing(uvm_processor_id_t preferred_location,
                                            page_thrashing_info_t *page_thrashing)
{
    if (UVM_ID_IS_INVALID(preferred_location))
        return false;

    return uvm_processor_mask_test(&page_thrashing->processors, preferred_location);
}

static uvm_perf_thrashing_hint_t get_hint_for_migration_thrashing(va_space_thrashing_info_t *va_space_thrashing,
                                                                  uvm_va_block_t *va_block,
                                                                  uvm_page_index_t page_index,
                                                                  page_thrashing_info_t *page_thrashing,
                                                                  uvm_processor_id_t requester)
{
    uvm_perf_thrashing_hint_t hint;
    uvm_processor_id_t closest_resident_id;
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    uvm_processor_id_t do_not_throttle_processor = page_thrashing->do_not_throttle_processor_id;
    uvm_processor_id_t pinned_residency = page_thrashing->pinned_residency_id;
    const uvm_va_policy_t *policy;
    uvm_processor_id_t preferred_location;

    policy = uvm_va_policy_get(va_block, uvm_va_block_cpu_page_address(va_block, page_index));

    preferred_location = policy->preferred_location;

    hint.type = UVM_PERF_THRASHING_HINT_TYPE_NONE;

    closest_resident_id = uvm_va_block_page_get_closest_resident(va_block, page_index, requester);
    if (uvm_va_block_is_hmm(va_block)) {
        // HMM pages always start out resident on the CPU but may not be
        // recorded in the va_block state because hmm_range_fault() or
        // similar functions haven't been called to get an accurate snapshot
        // of the Linux state. We can assume pages are CPU resident for the
        // purpose of deciding where to migrate to reduce thrashing.
        if (UVM_ID_IS_INVALID(closest_resident_id))
            closest_resident_id = UVM_ID_CPU;
    }
    else {
        UVM_ASSERT(UVM_ID_IS_VALID(closest_resident_id));
    }

    if (thrashing_processors_can_access(va_space, page_thrashing, preferred_location)) {
        // The logic in uvm_va_block_select_residency chooses the preferred
        // location if the requester can access it, so all processors should
        // naturally get mapped to the preferred without thrashing. However,
        // we can get here if preferred location was set after processors
        // started thrashing.
        //
        // TODO: Bug 2527408. Reset thrashing history when a user policy
        //       changes in a VA block.
        hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
        hint.pin.residency = preferred_location;
    }
    else if (!preferred_location_is_thrashing(preferred_location, page_thrashing) &&
             thrashing_processors_have_fast_access_to(va_space, page_thrashing, closest_resident_id)) {
        // This is a fast path for those scenarios in which all thrashing
        // processors have fast (NVLINK + native atomics) access to the current
        // residency. This is skipped if the preferred location is thrashing and
        // not accessible by the rest of thrashing processors. Otherwise, we
        // would be in the condition above.
        if (UVM_ID_IS_CPU(closest_resident_id)) {
            // On P9 systems, we prefer the CPU to map vidmem (since it can
            // cache it), so don't map the GPU to sysmem.
            if (UVM_ID_IS_GPU(requester)) {
                hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
                hint.pin.residency = requester;
            }
        }
        else {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
            hint.pin.residency = closest_resident_id;
        }
    }
    else if (uvm_id_equal(requester, preferred_location)) {
        if (page_thrashing->pinned) {
            // If the faulting processor is the preferred location, we can
            // only:
            // 1) Pin to the preferred location
            // 2) Throttle if it's pinned elsewhere and we are not the
            //    do_not_throttle_processor
            if (uvm_id_equal(preferred_location, pinned_residency) ||
                uvm_id_equal(preferred_location, do_not_throttle_processor)) {
                hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
                hint.pin.residency = preferred_location;
            }
            else {
                hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
            }
        }
        else if (!uvm_id_equal(preferred_location, do_not_throttle_processor)) {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
        }
        else if (page_thrashing->throttling_count >= va_space_thrashing->params.pin_threshold) {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
            hint.pin.residency = preferred_location;
        }
    }
    else if (page_thrashing->pinned) {
        // 1) If the requester is the do_not_throttle_processor pin it to the
        //    requester if all thrashing processors can access the requester,
        //    or to a common location, or to the requester anyway if no common
        //    location found.
        // 2) Try to map the current pinned residency.
        // 3) Throttle.
        if (uvm_id_equal(requester, do_not_throttle_processor)) {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;

            if (thrashing_processors_can_access(va_space, page_thrashing, requester)) {
                hint.pin.residency = requester;
            }
            else {
                uvm_processor_mask_t common_locations;

                thrashing_processors_common_locations(va_space, page_thrashing, &common_locations);
                if (uvm_processor_mask_empty(&common_locations)) {
                    hint.pin.residency = requester;
                }
                else {
                    // Find the common location that is closest to the requester
                    hint.pin.residency = uvm_processor_mask_find_closest_id(va_space, &common_locations, requester);
                }
            }
        }
        else if (uvm_processor_mask_test(&va_space->accessible_from[uvm_id_value(pinned_residency)], requester)) {
            if (!uvm_va_block_is_hmm(va_block))
                UVM_ASSERT(uvm_id_equal(closest_resident_id, pinned_residency));

            hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
            hint.pin.residency = pinned_residency;
        }
        else {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
        }
    }
    else if (!uvm_id_equal(requester, do_not_throttle_processor)) {
        hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
    }
    else if (page_thrashing->throttling_count >= va_space_thrashing->params.pin_threshold) {
        hint.type = UVM_PERF_THRASHING_HINT_TYPE_PIN;
        hint.pin.residency = requester;
    }

    if (hint.type == UVM_PERF_THRASHING_HINT_TYPE_PIN &&
        !uvm_va_space_processor_has_memory(va_space, hint.pin.residency))
        hint.pin.residency = UVM_ID_CPU;

    return hint;
}

// Function called on fault that tells the fault handler if any operation
// should be performed to minimize thrashing. The logic is as follows:
//
// - Phase0: Block thrashing. If a number of consecutive thrashing events have
//   been detected on the VA block, per-page thrashing tracking information is
//   created.
// - Phase1: Throttling. When several processors fight over a page, we start a
//   "throttling period". During that period, only one processor will be able
//   to service faults on the page, and the rest will be throttled. All CPU
//   faults are considered to belong to the same device, even if they come from
//   different CPU threads.
// - Phase2: Pinning. After a number of consecutive throttling periods, the page
//   is pinned on a specific processor which all of the thrashing processors can
//   access.
// - Phase3: Revocation throttling. Even if the page is pinned, it can be still
//   thrashing due to revocation events (mainly due to system-wide atomics). In
//   that case we keep the page pinned while applying the same algorithm as in
//   Phase1.
uvm_perf_thrashing_hint_t uvm_perf_thrashing_get_hint(uvm_va_block_t *va_block,
                                                      NvU64 address,
                                                      uvm_processor_id_t requester)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);
    block_thrashing_info_t *block_thrashing = NULL;
    page_thrashing_info_t *page_thrashing = NULL;
    uvm_perf_thrashing_hint_t hint;
    uvm_page_index_t page_index = uvm_va_block_cpu_page_index(va_block, address);
    NvU64 time_stamp;
    NvU64 last_time_stamp;

    hint.type = UVM_PERF_THRASHING_HINT_TYPE_NONE;

    if (!va_space_thrashing->params.enable)
        return hint;

    // If we don't have enough memory to store thrashing information, we assume
    // no thrashing
    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing)
        return hint;

    // If the per-page tracking structure has not been created yet, we assume
    // no thrashing
    if (!block_thrashing->pages)
        return hint;

    time_stamp = NV_GETTIME();

    if (block_thrashing->last_thrashing_time_stamp != 0 &&
        (time_stamp - block_thrashing->last_thrashing_time_stamp > va_space_thrashing->params.epoch_ns) &&
        block_thrashing->pinned_pages.count == 0 &&
        block_thrashing->thrashing_reset_count < va_space_thrashing->params.max_resets) {
        uvm_page_index_t reset_page_index;

        ++block_thrashing->thrashing_reset_count;

        // Clear the state of throttled processors to make sure that we flush
        // any pending ThrottlingEnd events
        for_each_va_block_page_in_mask(reset_page_index, &block_thrashing->thrashing_pages, va_block) {
            thrashing_throttling_reset_page(va_block,
                                            block_thrashing,
                                            &block_thrashing->pages[reset_page_index],
                                            reset_page_index);
        }

        // Reset per-page tracking structure
        // TODO: Bug 1769904 [uvm] Speculatively unpin pages that were pinned on a specific memory due to thrashing
        UVM_ASSERT(uvm_page_mask_empty(&block_thrashing->pinned_pages.mask));
        uvm_kvfree(block_thrashing->pages);
        block_thrashing->pages                     = NULL;
        block_thrashing->num_thrashing_pages       = 0;
        block_thrashing->last_processor            = UVM_ID_INVALID;
        block_thrashing->last_time_stamp           = 0;
        block_thrashing->last_thrashing_time_stamp = 0;
        uvm_page_mask_zero(&block_thrashing->thrashing_pages);
        goto done;
    }

    page_thrashing = &block_thrashing->pages[page_index];

    // Not enough thrashing events yet
    if (page_thrashing->num_thrashing_events < va_space_thrashing->params.threshold)
        goto done;

    // If the requesting processor is throttled, check the throttling end time
    // stamp
    if (uvm_processor_mask_test(&page_thrashing->throttled_processors, requester)) {
        NvU64 throttling_end_time_stamp = page_thrashing_get_throttling_end_time_stamp(page_thrashing);
        if (time_stamp < throttling_end_time_stamp &&
            !uvm_id_equal(requester, page_thrashing->do_not_throttle_processor_id)) {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
            goto done;
        }

        thrashing_throttle_end_processor(va_block, block_thrashing, page_thrashing, page_index, requester);
    }

    UVM_ASSERT(!uvm_processor_mask_test(&page_thrashing->throttled_processors, requester));

    last_time_stamp = page_thrashing_get_time_stamp(page_thrashing);

    // If the lapse since the last thrashing event is longer than a thrashing
    // lapse we are no longer thrashing
    if (time_stamp - last_time_stamp > va_space_thrashing->params.lapse_ns &&
        !page_thrashing->pinned) {
        goto done;
    }

    // Set the requesting processor in the thrashing processors mask
    uvm_processor_mask_set(&page_thrashing->processors, requester);

    UVM_ASSERT(page_thrashing->has_migration_events || page_thrashing->has_revocation_events);

    // Update throttling heuristics
    thrashing_throttle_update(va_space_thrashing, va_block, page_thrashing, requester, time_stamp);

    if (page_thrashing->pinned &&
        page_thrashing->has_revocation_events &&
        !uvm_id_equal(requester, page_thrashing->do_not_throttle_processor_id)) {

        // When we get revocation thrashing, this is due to system-wide atomics
        // downgrading the permissions of other processors. Revocations only
        // happen when several processors are mapping the same page and there
        // are no migrations. In this case, the only thing we can do is to
        // throttle the execution of the processors.
        hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
    }
    else {
        hint = get_hint_for_migration_thrashing(va_space_thrashing,
                                                va_block,
                                                page_index,
                                                page_thrashing,
                                                requester);
    }

done:
    if (hint.type == UVM_PERF_THRASHING_HINT_TYPE_PIN) {
        NV_STATUS status = thrashing_pin_page(va_space_thrashing,
                                              va_block,
                                              block_thrashing,
                                              page_thrashing,
                                              page_index,
                                              time_stamp,
                                              hint.pin.residency,
                                              requester);

        // If there was some problem pinning the page (i.e. OOM), demote to
        // throttling)
        if (status != NV_OK) {
            hint.type = UVM_PERF_THRASHING_HINT_TYPE_THROTTLE;
        }
        else {
            if (uvm_id_equal(hint.pin.residency, requester))
                PROCESSOR_THRASHING_STATS_INC(va_space, requester, num_pin_local);
            else
                PROCESSOR_THRASHING_STATS_INC(va_space, requester, num_pin_remote);

            uvm_processor_mask_copy(&hint.pin.processors, &page_thrashing->processors);
        }
    }

    if (hint.type == UVM_PERF_THRASHING_HINT_TYPE_THROTTLE) {
        thrashing_throttle_processor(va_block,
                                     block_thrashing,
                                     page_thrashing,
                                     page_index,
                                     requester);

        PROCESSOR_THRASHING_STATS_INC(va_space, requester, num_throttle);

        hint.throttle.end_time_stamp = page_thrashing_get_throttling_end_time_stamp(page_thrashing);
    }
    else if (hint.type == UVM_PERF_THRASHING_HINT_TYPE_NONE && page_thrashing) {
        UVM_ASSERT(!uvm_processor_mask_test(&page_thrashing->throttled_processors, requester));
        UVM_ASSERT(!page_thrashing->pinned);
        UVM_ASSERT(UVM_ID_IS_INVALID(page_thrashing->pinned_residency_id));
    }

    return hint;
}

uvm_processor_mask_t *uvm_perf_thrashing_get_thrashing_processors(uvm_va_block_t *va_block, NvU64 address)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);
    block_thrashing_info_t *block_thrashing = NULL;
    page_thrashing_info_t *page_thrashing = NULL;
    uvm_page_index_t page_index = uvm_va_block_cpu_page_index(va_block, address);

    UVM_ASSERT(g_uvm_perf_thrashing_enable);
    UVM_ASSERT(va_space_thrashing->params.enable);

    block_thrashing = thrashing_info_get(va_block);
    UVM_ASSERT(block_thrashing);

    UVM_ASSERT(block_thrashing->pages);

    page_thrashing = &block_thrashing->pages[page_index];

    return &page_thrashing->processors;
}

const uvm_page_mask_t *uvm_perf_thrashing_get_thrashing_pages(uvm_va_block_t *va_block)
{
    uvm_va_space_t *va_space = uvm_va_block_get_va_space(va_block);
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);
    block_thrashing_info_t *block_thrashing = NULL;

    if (!va_space_thrashing->params.enable)
        return NULL;

    block_thrashing = thrashing_info_get(va_block);
    if (!block_thrashing)
        return NULL;

    if (block_thrashing->num_thrashing_pages == 0)
        return NULL;

    return &block_thrashing->thrashing_pages;
}

#define TIMER_GRANULARITY_NS 20000ULL
static void thrashing_unpin_pages(struct work_struct *work)
{
    struct delayed_work *dwork = to_delayed_work(work);
    va_space_thrashing_info_t *va_space_thrashing = container_of(dwork, va_space_thrashing_info_t, pinned_pages.dwork);
    uvm_va_space_t *va_space = va_space_thrashing->va_space;
    uvm_va_block_context_t *va_block_context = va_space_thrashing->pinned_pages.va_block_context;

    // Take the VA space lock so that VA blocks don't go away during this
    // operation.
    uvm_va_space_down_read(va_space);

    if (va_space_thrashing->pinned_pages.in_va_space_teardown)
        goto exit_no_list_lock;

    while (1) {
        pinned_page_t *pinned_page;
        uvm_va_block_t *va_block;

        uvm_spin_lock(&va_space_thrashing->pinned_pages.lock);
        pinned_page = list_first_entry_or_null(&va_space_thrashing->pinned_pages.list,
                                               pinned_page_t,
                                               va_space_list_entry);

        if (pinned_page) {
            NvU64 now = NV_GETTIME();

            if (pinned_page->deadline <= (now + TIMER_GRANULARITY_NS)) {
                list_del_init(&pinned_page->va_space_list_entry);

                // Work cancellation is left to thrashing_unpin_page() as this
                // would only catch the following pattern:
                // - Worker thread A is in thrashing_unpin_pages but hasn't
                // looked at the list yet
                // - Thread B then removes the last entry
                // - Thread C then adds a new entry and re-schedules work
                // - Worker thread A removes the entry added by C because the
                // deadline has passed (unlikely), then cancels the work
                // scheduled by C.
            }
            else {
                NvU64 elapsed_us = (pinned_page->deadline - now) / 1000;

                schedule_delayed_work(&va_space_thrashing->pinned_pages.dwork, usecs_to_jiffies(elapsed_us));
                uvm_spin_unlock(&va_space_thrashing->pinned_pages.lock);
                break;
            }
        }

        uvm_spin_unlock(&va_space_thrashing->pinned_pages.lock);

        if (!pinned_page)
            break;

        va_block = pinned_page->va_block;
        if (uvm_va_block_is_hmm(va_block))
            uvm_hmm_migrate_begin_wait(va_block);
        uvm_mutex_lock(&va_block->lock);

        // Only operate if the pinned page's tracking state isn't already
        // cleared by thrashing_unpin_page()
        if (!list_empty(&pinned_page->va_block_list_entry)) {
            uvm_page_index_t page_index = pinned_page->page_index;
            block_thrashing_info_t *block_thrashing = thrashing_info_get(va_block);

            UVM_ASSERT(block_thrashing);
            UVM_ASSERT(uvm_page_mask_test(&block_thrashing->pinned_pages.mask, page_index));

            uvm_va_block_context_init(va_block_context, NULL);

            uvm_perf_thrashing_unmap_remote_pinned_pages_all(va_block,
                                                             va_block_context,
                                                             uvm_va_block_region_for_page(page_index));
            thrashing_reset_page(va_space_thrashing, va_block, block_thrashing, page_index);
        }

        uvm_mutex_unlock(&va_block->lock);
        if (uvm_va_block_is_hmm(va_block))
            uvm_hmm_migrate_finish(va_block);
        kmem_cache_free(g_pinned_page_cache, pinned_page);
    }

exit_no_list_lock:
    uvm_va_space_up_read(va_space);
}

static void thrashing_unpin_pages_entry(struct work_struct *work)
{
    UVM_ENTRY_VOID(thrashing_unpin_pages(work));
}

NV_STATUS uvm_perf_thrashing_load(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing;
    NV_STATUS status;

    status = uvm_perf_module_load(&g_module_thrashing, va_space);
    if (status != NV_OK)
        return status;

    va_space_thrashing = va_space_thrashing_info_create(va_space);
    if (!va_space_thrashing)
        return NV_ERR_NO_MEMORY;

    uvm_spin_lock_init(&va_space_thrashing->pinned_pages.lock, UVM_LOCK_ORDER_LEAF);
    INIT_LIST_HEAD(&va_space_thrashing->pinned_pages.list);
    INIT_DELAYED_WORK(&va_space_thrashing->pinned_pages.dwork, thrashing_unpin_pages_entry);

    return NV_OK;
}

void uvm_perf_thrashing_stop(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing;

    uvm_va_space_down_write(va_space);
    va_space_thrashing = va_space_thrashing_info_get_or_null(va_space);

    // Prevent further unpinning operations from being scheduled
    if (va_space_thrashing)
        va_space_thrashing->pinned_pages.in_va_space_teardown = true;

    uvm_va_space_up_write(va_space);

    // Cancel any pending work. We can safely access va_space_thrashing
    // because this function is called once from the VA space teardown path,
    // and the only function that frees it is uvm_perf_thrashing_unload,
    // which is called later in the teardown path.
    if (va_space_thrashing)
        (void)cancel_delayed_work_sync(&va_space_thrashing->pinned_pages.dwork);
}

void uvm_perf_thrashing_unload(uvm_va_space_t *va_space)
{
    va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get_or_null(va_space);

    uvm_perf_module_unload(&g_module_thrashing, va_space);

    // Make sure that there are not pending work items
    if (va_space_thrashing) {
        UVM_ASSERT(list_empty(&va_space_thrashing->pinned_pages.list));

        va_space_thrashing_info_destroy(va_space);
    }
}

NV_STATUS uvm_perf_thrashing_register_gpu(uvm_va_space_t *va_space, uvm_gpu_t *gpu)
{
    // If a simulated GPU is registered, re-initialize thrashing parameters in
    // case they need to be adjusted.
    bool params_need_readjusting = g_uvm_global.num_simulated_devices > 0;

    // Likewise, when the Confidential Computing feature is enabled, the DMA
    // path is slower due to cryptographic operations & other associated
    // overhead. Enforce a larger window to allow the thrashing mitigation
    // mechanisms to work properly.
    params_need_readjusting = params_need_readjusting || uvm_conf_computing_mode_enabled(gpu);

    if (params_need_readjusting) {
        va_space_thrashing_info_t *va_space_thrashing = va_space_thrashing_info_get(va_space);

        if (!va_space_thrashing->params.test_overrides) {
            if (uvm_conf_computing_mode_enabled(gpu))
                g_uvm_perf_thrashing_lapse_usec = UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT_HCC;

            va_space_thrashing_info_init_params(va_space_thrashing);
        }
    }

    return NV_OK;
}

NV_STATUS uvm_perf_thrashing_init(void)
{
    NV_STATUS status;

    INIT_THRASHING_PARAMETER_TOGGLE(uvm_perf_thrashing_enable, UVM_PERF_THRASHING_ENABLE_DEFAULT);
    if (!g_uvm_perf_thrashing_enable)
        return NV_OK;

    uvm_perf_module_init("perf_thrashing",
                         UVM_PERF_MODULE_TYPE_THRASHING,
                         g_callbacks_thrashing,
                         ARRAY_SIZE(g_callbacks_thrashing),
                         &g_module_thrashing);

    INIT_THRASHING_PARAMETER_NONZERO_MAX(uvm_perf_thrashing_threshold,
                                         UVM_PERF_THRASHING_THRESHOLD_DEFAULT,
                                         UVM_PERF_THRASHING_THRESHOLD_MAX);

    INIT_THRASHING_PARAMETER_NONZERO_MAX(uvm_perf_thrashing_pin_threshold,
                                         UVM_PERF_THRASHING_PIN_THRESHOLD_DEFAULT,
                                         UVM_PERF_THRASHING_PIN_THRESHOLD_MAX);

    INIT_THRASHING_PARAMETER_NONZERO(uvm_perf_thrashing_lapse_usec, UVM_PERF_THRASHING_LAPSE_USEC_DEFAULT);

    INIT_THRASHING_PARAMETER_NONZERO_MAX(uvm_perf_thrashing_nap,
                                         UVM_PERF_THRASHING_NAP_DEFAULT,
                                         UVM_PERF_THRASHING_NAP_MAX);


    INIT_THRASHING_PARAMETER_NONZERO(uvm_perf_thrashing_epoch, UVM_PERF_THRASHING_EPOCH_DEFAULT);

    INIT_THRASHING_PARAMETER(uvm_perf_thrashing_pin, UVM_PERF_THRASHING_PIN_DEFAULT);

    INIT_THRASHING_PARAMETER(uvm_perf_thrashing_max_resets, UVM_PERF_THRASHING_MAX_RESETS_DEFAULT);

    g_va_block_thrashing_info_cache = NV_KMEM_CACHE_CREATE("uvm_block_thrashing_info_t", block_thrashing_info_t);
    if (!g_va_block_thrashing_info_cache) {
        status = NV_ERR_NO_MEMORY;
        goto error;
    }

    g_pinned_page_cache = NV_KMEM_CACHE_CREATE("uvm_pinned_page_t", pinned_page_t);
    if (!g_pinned_page_cache) {
        status = NV_ERR_NO_MEMORY;
        goto error;
    }

    status = cpu_thrashing_stats_init();
    if (status != NV_OK)
        goto error;

    return NV_OK;

error:
    uvm_perf_thrashing_exit();

    return status;
}

void uvm_perf_thrashing_exit(void)
{
    cpu_thrashing_stats_exit();

    kmem_cache_destroy_safe(&g_va_block_thrashing_info_cache);
    kmem_cache_destroy_safe(&g_pinned_page_cache);
}

NV_STATUS uvm_perf_thrashing_add_gpu(uvm_gpu_t *gpu)
{
    if (!uvm_procfs_is_debug_enabled())
        return NV_OK;

    return gpu_thrashing_stats_create(gpu);
}

void uvm_perf_thrashing_remove_gpu(uvm_gpu_t *gpu)
{
    gpu_thrashing_stats_destroy(gpu);
}

NV_STATUS uvm_test_get_page_thrashing_policy(UVM_TEST_GET_PAGE_THRASHING_POLICY_PARAMS *params, struct file *filp)
{
    uvm_va_space_t *va_space = uvm_va_space_get(filp);
    va_space_thrashing_info_t *va_space_thrashing;

    uvm_va_space_down_read(va_space);

    va_space_thrashing = va_space_thrashing_info_get(va_space);

    if (va_space_thrashing->params.enable) {
        params->policy = UVM_TEST_PAGE_THRASHING_POLICY_ENABLE;
        params->nap_ns = va_space_thrashing->params.nap_ns;
        params->pin_ns = va_space_thrashing->params.pin_ns;
        params->map_remote_on_native_atomics_fault = uvm_perf_map_remote_on_native_atomics_fault != 0;
    }
    else {
        params->policy = UVM_TEST_PAGE_THRASHING_POLICY_DISABLE;
    }

    uvm_va_space_up_read(va_space);

    return NV_OK;
}

NV_STATUS uvm_test_set_page_thrashing_policy(UVM_TEST_SET_PAGE_THRASHING_POLICY_PARAMS *params, struct file *filp)
{
    NV_STATUS status = NV_OK;
    uvm_va_space_t *va_space = uvm_va_space_get(filp);
    va_space_thrashing_info_t *va_space_thrashing;

    if (params->policy >= UVM_TEST_PAGE_THRASHING_POLICY_MAX)
        return NV_ERR_INVALID_ARGUMENT;

    if (!g_uvm_perf_thrashing_enable)
        return NV_ERR_INVALID_STATE;

    uvm_va_space_down_write(va_space);

    va_space_thrashing = va_space_thrashing_info_get(va_space);
    va_space_thrashing->params.test_overrides = true;

    if (params->policy == UVM_TEST_PAGE_THRASHING_POLICY_ENABLE) {
        if (va_space_thrashing->params.enable)
            goto done_unlock_va_space;

        va_space_thrashing->params.pin_ns = params->pin_ns;
        va_space_thrashing->params.enable = true;
    }
    else {
        if (!va_space_thrashing->params.enable)
            goto done_unlock_va_space;

        va_space_thrashing->params.enable = false;
    }

    // When disabling thrashing detection, destroy the thrashing tracking
    // information for all VA blocks and unpin pages
    if (!va_space_thrashing->params.enable) {
        uvm_va_range_t *va_range;

        uvm_for_each_va_range(va_range, va_space) {
            uvm_va_block_t *va_block;

            if (va_range->type != UVM_VA_RANGE_TYPE_MANAGED)
                continue;

            for_each_va_block_in_va_range(va_range, va_block) {
                uvm_va_block_region_t va_block_region = uvm_va_block_region_from_block(va_block);
                uvm_va_block_context_t *block_context = uvm_va_space_block_context(va_space, NULL);

                uvm_mutex_lock(&va_block->lock);

                // Unmap may split PTEs and require a retry. Needs to be called
                // before the pinned pages information is destroyed.
                status = UVM_VA_BLOCK_RETRY_LOCKED(va_block, NULL,
                             uvm_perf_thrashing_unmap_remote_pinned_pages_all(va_block,
                                                                              block_context,
                                                                              va_block_region));

                uvm_perf_thrashing_info_destroy(va_block);

                uvm_mutex_unlock(&va_block->lock);

                // Re-enable thrashing on failure to avoid getting asserts
                // about having state while thrashing is disabled
                if (status != NV_OK) {
                    va_space_thrashing->params.enable = true;
                    goto done_unlock_va_space;
                }
            }
        }

        status = uvm_hmm_clear_thrashing_policy(va_space);

        // Re-enable thrashing on failure to avoid getting asserts
        // about having state while thrashing is disabled
        if (status != NV_OK) {
            va_space_thrashing->params.enable = true;
            goto done_unlock_va_space;
        }
    }

done_unlock_va_space:
    uvm_va_space_up_write(va_space);

    return status;
}