1 //=- CachePruning.h - Helper to manage the pruning of a cache dir -*- C++ -*-=//
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
7 //===----------------------------------------------------------------------===//
9 // This file implements pruning of a directory intended for cache storage, using
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_SUPPORT_CACHEPRUNING_H
15 #define LLVM_SUPPORT_CACHEPRUNING_H
17 #include "llvm/Support/MemoryBuffer.h"
23 template <typename T> class Expected;
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 std::nullopt
33 std::optional<std::chrono::seconds> Interval = std::chrono::seconds(1200);
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
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;
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;
52 /// The maximum number of files in the cache directory. A value of 0 disables
53 /// the number of files based pruning.
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;
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);
71 /// Peform pruning using the supplied policy, returns true if pruning
72 /// occurred, i.e. if Policy.Interval was expired.
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.
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 = {});