base/allocator/partition_allocator/partition_direct_map_extent.h

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_DIRECT_MAP_EXTENT_H_
#define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_DIRECT_MAP_EXTENT_H_

#include "base/allocator/partition_allocator/partition_alloc_base/compiler_specific.h"
#include "base/allocator/partition_allocator/partition_alloc_check.h"
#include "base/allocator/partition_allocator/partition_bucket.h"
#include "base/allocator/partition_allocator/partition_page.h"

namespace partition_alloc::internal {

template <bool thread_safe>
struct PartitionDirectMapExtent {
  PartitionDirectMapExtent<thread_safe>* next_extent;
  PartitionDirectMapExtent<thread_safe>* prev_extent;
  PartitionBucket<thread_safe>* bucket;
  // Size of the entire reservation, including guard pages, meta-data,
  // padding for alignment before allocation, and padding for granularity at the
  // end of the allocation.
  size_t reservation_size;
  // Padding between the first partition page (guard pages + meta-data) and
  // the allocation.
  size_t padding_for_alignment;

  PA_ALWAYS_INLINE static PartitionDirectMapExtent<thread_safe>* FromSlotSpan(
      SlotSpanMetadata<thread_safe>* slot_span);
};

// Metadata page for direct-mapped allocations.
template <bool thread_safe>
struct PartitionDirectMapMetadata {
  // |page| and |subsequent_page| are needed to match the layout of normal
  // buckets (specifically, of single-slot slot spans), with the caveat that
  // only the first subsequent page is needed (for SubsequentPageMetadata) and
  // others aren't used for direct map.
  PartitionPage<thread_safe> page;
  PartitionPage<thread_safe> subsequent_page;
  // The following fields are metadata specific to direct map allocations. All
  // these fields will easily fit into the precalculated metadata region,
  // because a direct map allocation starts no further than half way through the
  // super page.
  PartitionBucket<thread_safe> bucket;
  PartitionDirectMapExtent<thread_safe> direct_map_extent;

  PA_ALWAYS_INLINE static PartitionDirectMapMetadata<thread_safe>* FromSlotSpan(
      SlotSpanMetadata<thread_safe>* slot_span);
};

template <bool thread_safe>
PA_ALWAYS_INLINE PartitionDirectMapMetadata<thread_safe>*
PartitionDirectMapMetadata<thread_safe>::FromSlotSpan(
    SlotSpanMetadata<thread_safe>* slot_span) {
  PA_DCHECK(slot_span->bucket->is_direct_mapped());
  // |*slot_span| is the first field of |PartitionDirectMapMetadata|, just cast.
  auto* metadata =
      reinterpret_cast<PartitionDirectMapMetadata<thread_safe>*>(slot_span);
  PA_DCHECK(&metadata->page.slot_span_metadata == slot_span);
  return metadata;
}

template <bool thread_safe>
PA_ALWAYS_INLINE PartitionDirectMapExtent<thread_safe>*
PartitionDirectMapExtent<thread_safe>::FromSlotSpan(
    SlotSpanMetadata<thread_safe>* slot_span) {
  PA_DCHECK(slot_span->bucket->is_direct_mapped());
  return &PartitionDirectMapMetadata<thread_safe>::FromSlotSpan(slot_span)
              ->direct_map_extent;
}

}  // namespace partition_alloc::internal

#endif  // BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_DIRECT_MAP_EXTENT_H_