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Summary: 508 root node entries (root_limit) 510 internal node entries (node_limit) For a filename with 40 bytes, its sizeof(ext4_dir_entry_2) = 48, a linear directory can contain at most floor(4096/48)=85 of them. The real per-directory entry limit should be 508*510*85 = 22021800 The limit varies with the average length of filenames. However, the Linux ext4 code does not try rebalancing the htree, so we will not be able to create filenames in a full leaf node. This is demonstrated with the following example, certain filenames cannot be used while others can: % touch d/0000000000000000000000000000000000816a6f touch: cannot touch 'd/0000000000000000000000000000000000816a6f': No space left on device % touch d/0000000000000000000000000000000000816a70 # succeeded Reviewers: pcc Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D45546 llvm-svn: 329966
81 lines
3.5 KiB
C++
81 lines
3.5 KiB
C++
//=- CachePruning.h - Helper to manage the pruning of a cache dir -*- C++ -*-=//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements pruning of a directory intended for cache storage, using
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// various policies.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_CACHE_PRUNING_H
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#define LLVM_SUPPORT_CACHE_PRUNING_H
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#include "llvm/ADT/StringRef.h"
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#include <chrono>
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namespace llvm {
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template <typename T> class Expected;
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/// Policy for the pruneCache() function. A default constructed
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/// CachePruningPolicy provides a reasonable default policy.
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struct CachePruningPolicy {
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/// The pruning interval. This is intended to be used to avoid scanning the
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/// directory too often. It does not impact the decision of which file to
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/// prune. A value of 0 forces the scan to occur. A value of None disables
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/// pruning.
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llvm::Optional<std::chrono::seconds> Interval = std::chrono::seconds(1200);
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/// The expiration for a file. When a file hasn't been accessed for Expiration
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/// seconds, it is removed from the cache. A value of 0 disables the
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/// expiration-based pruning.
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std::chrono::seconds Expiration = std::chrono::hours(7 * 24); // 1w
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/// The maximum size for the cache directory, in terms of percentage of the
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/// available space on the disk. Set to 100 to indicate no limit, 50 to
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/// indicate that the cache size will not be left over half the available disk
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/// space. A value over 100 will be reduced to 100. A value of 0 disables the
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/// percentage size-based pruning.
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unsigned MaxSizePercentageOfAvailableSpace = 75;
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/// The maximum size for the cache directory in bytes. A value over the amount
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/// of available space on the disk will be reduced to the amount of available
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/// space. A value of 0 disables the absolute size-based pruning.
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uint64_t MaxSizeBytes = 0;
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/// The maximum number of files in the cache directory. A value of 0 disables
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/// the number of files based pruning.
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///
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/// This defaults to 1000000 because with that many files there are
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/// diminishing returns on the effectiveness of the cache. Some systems have a
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/// limit on total number of files, and some also limit the number of files
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/// per directory, such as Linux ext4, with the default setting (block size is
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/// 4096 and large_dir disabled), there is a per-directory entry limit of
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/// 508*510*floor(4096/(40+8))~=20M for average filename length of 40.
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uint64_t MaxSizeFiles = 1000000;
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};
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/// Parse the given string as a cache pruning policy. Defaults are taken from a
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/// default constructed CachePruningPolicy object.
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/// For example: "prune_interval=30s:prune_after=24h:cache_size=50%"
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/// which means a pruning interval of 30 seconds, expiration time of 24 hours
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/// and maximum cache size of 50% of available disk space.
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Expected<CachePruningPolicy> parseCachePruningPolicy(StringRef PolicyStr);
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/// Peform pruning using the supplied policy, returns true if pruning
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/// occurred, i.e. if Policy.Interval was expired.
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///
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/// As a safeguard against data loss if the user specifies the wrong directory
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/// as their cache directory, this function will ignore files not matching the
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/// pattern "llvmcache-*".
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bool pruneCache(StringRef Path, CachePruningPolicy Policy);
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} // namespace llvm
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#endif
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