1 //=- CachePruning.h - Helper to manage the pruning of a cache dir -*- C++ -*-=// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements pruning of a directory intended for cache storage, using 10 // various policies. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_SUPPORT_CACHEPRUNING_H 15 #define LLVM_SUPPORT_CACHEPRUNING_H 16 17 #include "llvm/Support/MemoryBuffer.h" 18 #include <chrono> 19 #include <optional> 20 21 namespace llvm { 22 23 template <typename T> class Expected; 24 class StringRef; 25 26 /// Policy for the pruneCache() function. A default constructed 27 /// CachePruningPolicy provides a reasonable default policy. 28 struct CachePruningPolicy { 29 /// The pruning interval. This is intended to be used to avoid scanning the 30 /// directory too often. It does not impact the decision of which file to 31 /// prune. A value of 0 forces the scan to occur. A value of None disables 32 /// pruning. 33 std::optional<std::chrono::seconds> Interval = std::chrono::seconds(1200); 34 35 /// The expiration for a file. When a file hasn't been accessed for Expiration 36 /// seconds, it is removed from the cache. A value of 0 disables the 37 /// expiration-based pruning. 38 std::chrono::seconds Expiration = std::chrono::hours(7 * 24); // 1w 39 40 /// The maximum size for the cache directory, in terms of percentage of the 41 /// available space on the disk. Set to 100 to indicate no limit, 50 to 42 /// indicate that the cache size will not be left over half the available disk 43 /// space. A value over 100 will be reduced to 100. A value of 0 disables the 44 /// percentage size-based pruning. 45 unsigned MaxSizePercentageOfAvailableSpace = 75; 46 47 /// The maximum size for the cache directory in bytes. A value over the amount 48 /// of available space on the disk will be reduced to the amount of available 49 /// space. A value of 0 disables the absolute size-based pruning. 50 uint64_t MaxSizeBytes = 0; 51 52 /// The maximum number of files in the cache directory. A value of 0 disables 53 /// the number of files based pruning. 54 /// 55 /// This defaults to 1000000 because with that many files there are 56 /// diminishing returns on the effectiveness of the cache. Some systems have a 57 /// limit on total number of files, and some also limit the number of files 58 /// per directory, such as Linux ext4, with the default setting (block size is 59 /// 4096 and large_dir disabled), there is a per-directory entry limit of 60 /// 508*510*floor(4096/(40+8))~=20M for average filename length of 40. 61 uint64_t MaxSizeFiles = 1000000; 62 }; 63 64 /// Parse the given string as a cache pruning policy. Defaults are taken from a 65 /// default constructed CachePruningPolicy object. 66 /// For example: "prune_interval=30s:prune_after=24h:cache_size=50%" 67 /// which means a pruning interval of 30 seconds, expiration time of 24 hours 68 /// and maximum cache size of 50% of available disk space. 69 Expected<CachePruningPolicy> parseCachePruningPolicy(StringRef PolicyStr); 70 71 /// Peform pruning using the supplied policy, returns true if pruning 72 /// occurred, i.e. if Policy.Interval was expired. 73 /// 74 /// Check whether cache pruning happens using the supplied policy, adds a 75 /// ThinLTO warning if cache_size_bytes or cache_size_files is too small for the 76 /// current link job. The warning recommends the user to consider adjusting 77 /// --thinlto-cache-policy. 78 /// 79 /// As a safeguard against data loss if the user specifies the wrong directory 80 /// as their cache directory, this function will ignore files not matching the 81 /// pattern "llvmcache-*". 82 bool pruneCache(StringRef Path, CachePruningPolicy Policy, 83 const std::vector<std::unique_ptr<MemoryBuffer>> &Files = {}); 84 } // namespace llvm 85 86 #endif 87