diff options
Diffstat (limited to 'third_party/base/allocator/partition_allocator/partition_alloc_constants.h')
| -rw-r--r-- | third_party/base/allocator/partition_allocator/partition_alloc_constants.h | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/third_party/base/allocator/partition_allocator/partition_alloc_constants.h b/third_party/base/allocator/partition_allocator/partition_alloc_constants.h new file mode 100644 index 0000000000..cd9108cec2 --- /dev/null +++ b/third_party/base/allocator/partition_allocator/partition_alloc_constants.h @@ -0,0 +1,169 @@ +// Copyright (c) 2018 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONSTANTS_H_ +#define THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONSTANTS_H_ + +#include <limits.h> + +#include "third_party/base/allocator/partition_allocator/page_allocator_constants.h" +#include "third_party/base/logging.h" + +namespace pdfium { +namespace base { + +// Allocation granularity of sizeof(void*) bytes. +static const size_t kAllocationGranularity = sizeof(void*); +static const size_t kAllocationGranularityMask = kAllocationGranularity - 1; +static const size_t kBucketShift = (kAllocationGranularity == 8) ? 3 : 2; + +// Underlying partition storage pages are a power-of-two size. It is typical +// for a partition page to be based on multiple system pages. Most references to +// "page" refer to partition pages. +// We also have the concept of "super pages" -- these are the underlying system +// allocations we make. Super pages contain multiple partition pages inside them +// and include space for a small amount of metadata per partition page. +// Inside super pages, we store "slot spans". A slot span is a continguous range +// of one or more partition pages that stores allocations of the same size. +// Slot span sizes are adjusted depending on the allocation size, to make sure +// the packing does not lead to unused (wasted) space at the end of the last +// system page of the span. For our current max slot span size of 64k and other +// constant values, we pack _all_ PartitionRootGeneric::Alloc() sizes perfectly +// up against the end of a system page. +#if defined(_MIPS_ARCH_LOONGSON) +static const size_t kPartitionPageShift = 16; // 64KB +#else +static const size_t kPartitionPageShift = 14; // 16KB +#endif +static const size_t kPartitionPageSize = 1 << kPartitionPageShift; +static const size_t kPartitionPageOffsetMask = kPartitionPageSize - 1; +static const size_t kPartitionPageBaseMask = ~kPartitionPageOffsetMask; +static const size_t kMaxPartitionPagesPerSlotSpan = 4; + +// To avoid fragmentation via never-used freelist entries, we hand out partition +// freelist sections gradually, in units of the dominant system page size. +// What we're actually doing is avoiding filling the full partition page (16 KB) +// with freelist pointers right away. Writing freelist pointers will fault and +// dirty a private page, which is very wasteful if we never actually store +// objects there. +static const size_t kNumSystemPagesPerPartitionPage = + kPartitionPageSize / kSystemPageSize; +static const size_t kMaxSystemPagesPerSlotSpan = + kNumSystemPagesPerPartitionPage * kMaxPartitionPagesPerSlotSpan; + +// We reserve virtual address space in 2MB chunks (aligned to 2MB as well). +// These chunks are called "super pages". We do this so that we can store +// metadata in the first few pages of each 2MB aligned section. This leads to +// a very fast free(). We specifically choose 2MB because this virtual address +// block represents a full but single PTE allocation on ARM, ia32 and x64. +// +// The layout of the super page is as follows. The sizes below are the same +// for 32 bit and 64 bit. +// +// | Guard page (4KB) | +// | Metadata page (4KB) | +// | Guard pages (8KB) | +// | Slot span | +// | Slot span | +// | ... | +// | Slot span | +// | Guard page (4KB) | +// +// - Each slot span is a contiguous range of one or more PartitionPages. +// - The metadata page has the following format. Note that the PartitionPage +// that is not at the head of a slot span is "unused". In other words, +// the metadata for the slot span is stored only in the first PartitionPage +// of the slot span. Metadata accesses to other PartitionPages are +// redirected to the first PartitionPage. +// +// | SuperPageExtentEntry (32B) | +// | PartitionPage of slot span 1 (32B, used) | +// | PartitionPage of slot span 1 (32B, unused) | +// | PartitionPage of slot span 1 (32B, unused) | +// | PartitionPage of slot span 2 (32B, used) | +// | PartitionPage of slot span 3 (32B, used) | +// | ... | +// | PartitionPage of slot span N (32B, unused) | +// +// A direct mapped page has a similar layout to fake it looking like a super +// page: +// +// | Guard page (4KB) | +// | Metadata page (4KB) | +// | Guard pages (8KB) | +// | Direct mapped object | +// | Guard page (4KB) | +// +// - The metadata page has the following layout: +// +// | SuperPageExtentEntry (32B) | +// | PartitionPage (32B) | +// | PartitionBucket (32B) | +// | PartitionDirectMapExtent (8B) | +static const size_t kSuperPageShift = 21; // 2MB +static const size_t kSuperPageSize = 1 << kSuperPageShift; +static const size_t kSuperPageOffsetMask = kSuperPageSize - 1; +static const size_t kSuperPageBaseMask = ~kSuperPageOffsetMask; +static const size_t kNumPartitionPagesPerSuperPage = + kSuperPageSize / kPartitionPageSize; + +// The following kGeneric* constants apply to the generic variants of the API. +// The "order" of an allocation is closely related to the power-of-two size of +// the allocation. More precisely, the order is the bit index of the +// most-significant-bit in the allocation size, where the bit numbers starts +// at index 1 for the least-significant-bit. +// In terms of allocation sizes, order 0 covers 0, order 1 covers 1, order 2 +// covers 2->3, order 3 covers 4->7, order 4 covers 8->15. +static const size_t kGenericMinBucketedOrder = 4; // 8 bytes. +static const size_t kGenericMaxBucketedOrder = + 20; // Largest bucketed order is 1<<(20-1) (storing 512KB -> almost 1MB) +static const size_t kGenericNumBucketedOrders = + (kGenericMaxBucketedOrder - kGenericMinBucketedOrder) + 1; +// Eight buckets per order (for the higher orders), e.g. order 8 is 128, 144, +// 160, ..., 240: +static const size_t kGenericNumBucketsPerOrderBits = 3; +static const size_t kGenericNumBucketsPerOrder = + 1 << kGenericNumBucketsPerOrderBits; +static const size_t kGenericNumBuckets = + kGenericNumBucketedOrders * kGenericNumBucketsPerOrder; +static const size_t kGenericSmallestBucket = 1 + << (kGenericMinBucketedOrder - 1); +static const size_t kGenericMaxBucketSpacing = + 1 << ((kGenericMaxBucketedOrder - 1) - kGenericNumBucketsPerOrderBits); +static const size_t kGenericMaxBucketed = + (1 << (kGenericMaxBucketedOrder - 1)) + + ((kGenericNumBucketsPerOrder - 1) * kGenericMaxBucketSpacing); +static const size_t kGenericMinDirectMappedDownsize = + kGenericMaxBucketed + + 1; // Limit when downsizing a direct mapping using realloc(). +static const size_t kGenericMaxDirectMapped = + (1UL << 31) + kPageAllocationGranularity; // 2 GB plus one more page. +static const size_t kBitsPerSizeT = sizeof(void*) * CHAR_BIT; + +// Constant for the memory reclaim logic. +static const size_t kMaxFreeableSpans = 16; + +// If the total size in bytes of allocated but not committed pages exceeds this +// value (probably it is a "out of virtual address space" crash), +// a special crash stack trace is generated at |PartitionOutOfMemory|. +// This is to distinguish "out of virtual address space" from +// "out of physical memory" in crash reports. +static const size_t kReasonableSizeOfUnusedPages = 1024 * 1024 * 1024; // 1GB + +// These two byte values match tcmalloc. +static const unsigned char kUninitializedByte = 0xAB; +static const unsigned char kFreedByte = 0xCD; + +// Flags for PartitionAllocGenericFlags. +enum PartitionAllocFlags { + PartitionAllocReturnNull = 1 << 0, + PartitionAllocZeroFill = 1 << 1, + + PartitionAllocLastFlag = PartitionAllocZeroFill +}; + +} // namespace base +} // namespace pdfium + +#endif // THIRD_PARTY_BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONSTANTS_H_ |