third_party/base/allocator/partition_allocator/partition_alloc_constants.h - pdfium - Git at Google

 // 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 (`PartitionPage`s) are a power-of-2 size.
 // It is typical for a `PartitionPage` to be based on multiple system pages.
 // Most references to "page" refer to `PartitionPage`s.
 //
 // *Super pages* are the underlying system allocations we make. Super pages
 // contain multiple partition pages 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 `PartitionPage`s 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 maximum slot span size of 64 KiB 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;  // 64 KiB
 #else
 static const size_t kPartitionPageShift = 14;  // 16 KiB
 #endif
 static const size_t kPartitionPageSize = 1 << kPartitionPageShift;
 static const size_t kPartitionPageOffsetMask = kPartitionPageSize - 1;
 static const size_t kPartitionPageBaseMask = ~kPartitionPageOffsetMask;
 // TODO: Should this be 1 if defined(_MIPS_ARCH_LOONGSON)?
 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 `PartitionPage` (16 KiB)
 // 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 2 MiB chunks (aligned to 2 MiB as well).
 // These chunks are called *super pages*. We do this so that we can store
 // metadata in the first few pages of each 2 MiB-aligned section. This makes
 // freeing memory very fast. We specifically choose 2 MiB 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- and 64-bit platforms.
 //
 //     +-----------------------+
 //     | Guard page (4 KiB)    |
 //     | Metadata page (4 KiB) |
 //     | Guard pages (8 KiB)   |
 //     | Slot span             |
 //     | Slot span             |
 //     | ...                   |
 //     | Slot span             |
 //     | Guard page (4 KiB)    |
 //     +-----------------------+
 //
 // Each slot span is a contiguous range of one or more `PartitionPage`s.
 //
 // 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 `PartitionPage`s are redirected to the
 // first `PartitionPage`.
 //
 //     +---------------------------------------------+
 //     | SuperPageExtentEntry (32 B)                 |
 //     | PartitionPage of slot span 1 (32 B, used)   |
 //     | PartitionPage of slot span 1 (32 B, unused) |
 //     | PartitionPage of slot span 1 (32 B, unused) |
 //     | PartitionPage of slot span 2 (32 B, used)   |
 //     | PartitionPage of slot span 3 (32 B, used)   |
 //     | ...                                         |
 //     | PartitionPage of slot span N (32 B, unused) |
 //     +---------------------------------------------+
 //
 // A direct-mapped page has a similar layout to fake it looking like a super
 // page:
 //
 //     +-----------------------+
 //     | Guard page (4 KiB)    |
 //     | Metadata page (4 KiB) |
 //     | Guard pages (8 KiB)   |
 //     | Direct mapped object  |
 //     | Guard page (4 KiB)    |
 //     +-----------------------+
 //
 // A direct-mapped page's metadata page has the following layout:
 //
 //     +--------------------------------+
 //     | SuperPageExtentEntry (32 B)    |
 //     | PartitionPage (32 B)           |
 //     | PartitionBucket (32 B)         |
 //     | PartitionDirectMapExtent (8 B) |
 //     +--------------------------------+

 static const size_t kSuperPageShift = 21;  // 2 MiB
 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-1 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.
 // The largest bucketed order is 1 << (20 - 1), storing [512 KiB, 1 MiB):
 static const size_t kGenericMaxBucketedOrder = 20;
 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);
 // Limit when downsizing a direct mapping using `realloc`:
 static const size_t kGenericMinDirectMappedDownsize = kGenericMaxBucketed + 1;
 static const size_t kGenericMaxDirectMapped =
     (1UL << 31) + kPageAllocationGranularity;  // 2 GiB plus 1 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
 // `PartitionOutOfMemoryWithLotsOfUncommitedPages`. 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;  // 1 GiB

 // These 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_
	// 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 (`PartitionPage`s) are a power-of-2 size.
	// It is typical for a `PartitionPage` to be based on multiple system pages.
	// Most references to "page" refer to `PartitionPage`s.
	//
	// Super pages are the underlying system allocations we make. Super pages
	// contain multiple partition pages 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 `PartitionPage`s 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 maximum slot span size of 64 KiB 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; // 64 KiB
	#else
	static const size_t kPartitionPageShift = 14; // 16 KiB
	#endif
	static const size_t kPartitionPageSize = 1 << kPartitionPageShift;
	static const size_t kPartitionPageOffsetMask = kPartitionPageSize - 1;
	static const size_t kPartitionPageBaseMask = ~kPartitionPageOffsetMask;
	// TODO: Should this be 1 if defined(_MIPS_ARCH_LOONGSON)?
	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 `PartitionPage` (16 KiB)
	// 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 2 MiB chunks (aligned to 2 MiB as well).
	// These chunks are called super pages. We do this so that we can store
	// metadata in the first few pages of each 2 MiB-aligned section. This makes
	// freeing memory very fast. We specifically choose 2 MiB 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- and 64-bit platforms.
	//
	// +-----------------------+
	// \| Guard page (4 KiB) \|
	// \| Metadata page (4 KiB) \|
	// \| Guard pages (8 KiB) \|
	// \| Slot span \|
	// \| Slot span \|
	// \| ... \|
	// \| Slot span \|
	// \| Guard page (4 KiB) \|
	// +-----------------------+
	//
	// Each slot span is a contiguous range of one or more `PartitionPage`s.
	//
	// 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 `PartitionPage`s are redirected to the
	// first `PartitionPage`.
	//
	// +---------------------------------------------+
	// \| SuperPageExtentEntry (32 B) \|
	// \| PartitionPage of slot span 1 (32 B, used) \|
	// \| PartitionPage of slot span 1 (32 B, unused) \|
	// \| PartitionPage of slot span 1 (32 B, unused) \|
	// \| PartitionPage of slot span 2 (32 B, used) \|
	// \| PartitionPage of slot span 3 (32 B, used) \|
	// \| ... \|
	// \| PartitionPage of slot span N (32 B, unused) \|
	// +---------------------------------------------+
	//
	// A direct-mapped page has a similar layout to fake it looking like a super
	// page:
	//
	// +-----------------------+
	// \| Guard page (4 KiB) \|
	// \| Metadata page (4 KiB) \|
	// \| Guard pages (8 KiB) \|
	// \| Direct mapped object \|
	// \| Guard page (4 KiB) \|
	// +-----------------------+
	//
	// A direct-mapped page's metadata page has the following layout:
	//
	// +--------------------------------+
	// \| SuperPageExtentEntry (32 B) \|
	// \| PartitionPage (32 B) \|
	// \| PartitionBucket (32 B) \|
	// \| PartitionDirectMapExtent (8 B) \|
	// +--------------------------------+

	static const size_t kSuperPageShift = 21; // 2 MiB
	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-1 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.
	// The largest bucketed order is 1 << (20 - 1), storing [512 KiB, 1 MiB):
	static const size_t kGenericMaxBucketedOrder = 20;
	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);
	// Limit when downsizing a direct mapping using `realloc`:
	static const size_t kGenericMinDirectMappedDownsize = kGenericMaxBucketed + 1;
	static const size_t kGenericMaxDirectMapped =
	(1UL << 31) + kPageAllocationGranularity; // 2 GiB plus 1 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
	// `PartitionOutOfMemoryWithLotsOfUncommitedPages`. 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; // 1 GiB

	// These 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_