include/llvm/Support/CachePruning.h

   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