1 /* 2 * Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC. 3 * Copyright (C) 2007 The Regents of the University of California. 4 * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER). 5 * Written by Brian Behlendorf <behlendorf1@llnl.gov>. 6 * UCRL-CODE-235197 7 * 8 * This file is part of the SPL, Solaris Porting Layer. 9 * For details, see <http://zfsonlinux.org/>. 10 * 11 * The SPL is free software; you can redistribute it and/or modify it 12 * under the terms of the GNU General Public License as published by the 13 * Free Software Foundation; either version 2 of the License, or (at your 14 * option) any later version. 15 * 16 * The SPL is distributed in the hope that it will be useful, but WITHOUT 17 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 18 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 19 * for more details. 20 * 21 * You should have received a copy of the GNU General Public License along 22 * with the SPL. If not, see <http://www.gnu.org/licenses/>. 23 */ 24 25 #ifndef _SPL_VMEM_H 26 #define _SPL_VMEM_H 27 28 #include <sys/kmem.h> 29 #include <linux/sched.h> 30 #include <linux/vmalloc.h> 31 32 typedef struct vmem { } vmem_t; 33 34 /* 35 * Memory allocation interfaces 36 */ 37 #define VMEM_ALLOC 0x01 38 #define VMEM_FREE 0x02 39 40 #ifndef VMALLOC_TOTAL 41 #define VMALLOC_TOTAL (VMALLOC_END - VMALLOC_START) 42 #endif 43 44 /* 45 * vmem_* is an interface to a low level arena-based memory allocator on 46 * Illumos that is used to allocate virtual address space. The kmem SLAB 47 * allocator allocates slabs from it. Then the generic allocation functions 48 * kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators. 49 * 50 * On Linux, the primary means of doing allocations is via kmalloc(), which 51 * is similarly layered on top of something called the buddy allocator. The 52 * buddy allocator is not available to kernel modules, it uses physical 53 * memory addresses rather than virtual memory addresses and is prone to 54 * fragmentation. 55 * 56 * Linux sets aside a relatively small address space for in-kernel virtual 57 * memory from which allocations can be done using vmalloc(). It might seem 58 * like a good idea to use vmalloc() to implement something similar to 59 * Illumos' allocator. However, this has the following problems: 60 * 61 * 1. Page directory table allocations are hard coded to use GFP_KERNEL. 62 * Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using 63 * vmalloc() will not have proper semantics. 64 * 65 * 2. Address space exhaustion is a real issue on 32-bit platforms where 66 * only a few 100MB are available. The kernel will handle it by spinning 67 * when it runs out of address space. 68 * 69 * 3. All vmalloc() allocations and frees are protected by a single global 70 * lock which serializes all allocations. 71 * 72 * 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire 73 * list. The former will sum the allocations while the latter will print 74 * them to user space in a way that user space can keep the lock held 75 * indefinitely. When the total number of mapped allocations is large 76 * (several 100,000) a large amount of time will be spent waiting on locks. 77 * 78 * 5. Linux has a wait_on_bit() locking primitive that assumes physical 79 * memory is used, it simply does not work on virtual memory. Certain 80 * Linux structures (e.g. the superblock) use them and might be embedded 81 * into a structure from Illumos. This makes using Linux virtual memory 82 * unsafe in certain situations. 83 * 84 * It follows that we cannot obtain identical semantics to those on Illumos. 85 * Consequently, we implement the kmem_{alloc,zalloc,free}() functions in 86 * such a way that they can be used as drop-in replacements for small vmem_* 87 * allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}() 88 * to them. 89 */ 90 91 #define vmem_alloc(sz, fl) spl_vmem_alloc((sz), (fl), __func__, __LINE__) 92 #define vmem_zalloc(sz, fl) spl_vmem_zalloc((sz), (fl), __func__, __LINE__) 93 #define vmem_free(ptr, sz) spl_vmem_free((ptr), (sz)) 94 95 extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line); 96 extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line); 97 extern void spl_vmem_free(const void *ptr, size_t sz); 98 99 int spl_vmem_init(void); 100 void spl_vmem_fini(void); 101 102 #endif /* _SPL_VMEM_H */ 103