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_CACHE_PRUNING_H 15 #define LLVM_SUPPORT_CACHE_PRUNING_H 16 17 #include "llvm/ADT/StringRef.h" 18 #include <chrono> 19 20 namespace llvm { 21 22 template <typename T> class Expected; 23 24 /// Policy for the pruneCache() function. A default constructed 25 /// CachePruningPolicy provides a reasonable default policy. 26 struct CachePruningPolicy { 27 /// The pruning interval. This is intended to be used to avoid scanning the 28 /// directory too often. It does not impact the decision of which file to 29 /// prune. A value of 0 forces the scan to occur. A value of None disables 30 /// pruning. 31 llvm::Optional<std::chrono::seconds> Interval = std::chrono::seconds(1200); 32 33 /// The expiration for a file. When a file hasn't been accessed for Expiration 34 /// seconds, it is removed from the cache. A value of 0 disables the 35 /// expiration-based pruning. 36 std::chrono::seconds Expiration = std::chrono::hours(7 * 24); // 1w 37 38 /// The maximum size for the cache directory, in terms of percentage of the 39 /// available space on the disk. Set to 100 to indicate no limit, 50 to 40 /// indicate that the cache size will not be left over half the available disk 41 /// space. A value over 100 will be reduced to 100. A value of 0 disables the 42 /// percentage size-based pruning. 43 unsigned MaxSizePercentageOfAvailableSpace = 75; 44 45 /// The maximum size for the cache directory in bytes. A value over the amount 46 /// of available space on the disk will be reduced to the amount of available 47 /// space. A value of 0 disables the absolute size-based pruning. 48 uint64_t MaxSizeBytes = 0; 49 50 /// The maximum number of files in the cache directory. A value of 0 disables 51 /// the number of files based pruning. 52 /// 53 /// This defaults to 1000000 because with that many files there are 54 /// diminishing returns on the effectiveness of the cache. Some systems have a 55 /// limit on total number of files, and some also limit the number of files 56 /// per directory, such as Linux ext4, with the default setting (block size is 57 /// 4096 and large_dir disabled), there is a per-directory entry limit of 58 /// 508*510*floor(4096/(40+8))~=20M for average filename length of 40. 59 uint64_t MaxSizeFiles = 1000000; 60 }; 61 62 /// Parse the given string as a cache pruning policy. Defaults are taken from a 63 /// default constructed CachePruningPolicy object. 64 /// For example: "prune_interval=30s:prune_after=24h:cache_size=50%" 65 /// which means a pruning interval of 30 seconds, expiration time of 24 hours 66 /// and maximum cache size of 50% of available disk space. 67 Expected<CachePruningPolicy> parseCachePruningPolicy(StringRef PolicyStr); 68 69 /// Peform pruning using the supplied policy, returns true if pruning 70 /// occurred, i.e. if Policy.Interval was expired. 71 /// 72 /// As a safeguard against data loss if the user specifies the wrong directory 73 /// as their cache directory, this function will ignore files not matching the 74 /// pattern "llvmcache-*". 75 bool pruneCache(StringRef Path, CachePruningPolicy Policy); 76 77 } // namespace llvm 78 79 #endif 80