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 std::nullopt |
32 | /// disables 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 | |