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https://github.com/golang/go
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97 lines
2.9 KiB
C
97 lines
2.9 KiB
C
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Free(v) must be able to determine the MSpan containing v.
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// The MHeapMap is a 3-level radix tree mapping page numbers to MSpans.
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//
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// NOTE(rsc): On a 32-bit platform (= 20-bit page numbers),
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// we can swap in a 2-level radix tree.
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//
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// NOTE(rsc): We use a 3-level tree because tcmalloc does, but
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// having only three levels requires approximately 1 MB per node
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// in the tree, making the minimum map footprint 3 MB.
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// Using a 4-level tree would cut the minimum footprint to 256 kB.
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// On the other hand, it's just virtual address space: most of
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// the memory is never going to be touched, thus never paged in.
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typedef struct MHeapMapNode2 MHeapMapNode2;
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typedef struct MHeapMapNode3 MHeapMapNode3;
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enum
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{
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// 64 bit address - 12 bit page size = 52 bits to map
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MHeapMap_Level1Bits = 18,
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MHeapMap_Level2Bits = 18,
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MHeapMap_Level3Bits = 16,
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MHeapMap_TotalBits =
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MHeapMap_Level1Bits +
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MHeapMap_Level2Bits +
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MHeapMap_Level3Bits,
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MHeapMap_Level1Mask = (1<<MHeapMap_Level1Bits) - 1,
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MHeapMap_Level2Mask = (1<<MHeapMap_Level2Bits) - 1,
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MHeapMap_Level3Mask = (1<<MHeapMap_Level3Bits) - 1,
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};
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struct MHeapMap
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{
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void *(*allocator)(uintptr);
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MHeapMapNode2 *p[1<<MHeapMap_Level1Bits];
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};
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struct MHeapMapNode2
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{
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MHeapMapNode3 *p[1<<MHeapMap_Level2Bits];
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};
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struct MHeapMapNode3
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{
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MSpan *s[1<<MHeapMap_Level3Bits];
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};
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void MHeapMap_Init(MHeapMap *m, void *(*allocator)(uintptr));
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bool MHeapMap_Preallocate(MHeapMap *m, PageID k, uintptr npages);
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MSpan* MHeapMap_Get(MHeapMap *m, PageID k);
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MSpan* MHeapMap_GetMaybe(MHeapMap *m, PageID k);
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void MHeapMap_Set(MHeapMap *m, PageID k, MSpan *v);
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// Much of the time, free(v) needs to know only the size class for v,
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// not which span it came from. The MHeapMap finds the size class
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// by looking up the span.
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//
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// An MHeapMapCache is a simple direct-mapped cache translating
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// page numbers to size classes. It avoids the expensive MHeapMap
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// lookup for hot pages.
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//
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// The cache entries are 64 bits, with the page number in the low part
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// and the value at the top.
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//
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// NOTE(rsc): On a machine with 32-bit addresses (= 20-bit page numbers),
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// we can use a 16-bit cache entry by not storing the redundant 12 bits
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// of the key that are used as the entry index. Here in 64-bit land,
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// that trick won't work unless the hash table has 2^28 entries.
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enum
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{
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MHeapMapCache_HashBits = 12
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};
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struct MHeapMapCache
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{
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uintptr array[1<<MHeapMapCache_HashBits];
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};
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// All macros for speed (sorry).
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#define HMASK ((1<<MHeapMapCache_HashBits)-1)
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#define KBITS MHeapMap_TotalBits
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#define KMASK ((1LL<<KBITS)-1)
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#define MHeapMapCache_SET(cache, key, value) \
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((cache)->array[(key) & HMASK] = (key) | ((uintptr)(value) << KBITS))
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#define MHeapMapCache_GET(cache, key, tmp) \
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(tmp = (cache)->array[(key) & HMASK], \
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(tmp & KMASK) == (key) ? (tmp >> KBITS) : 0)
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