path: root/third_party/tcmalloc/chromium/src/page_heap.h

// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Sanjay Ghemawat <opensource@google.com>

#ifndef TCMALLOC_PAGE_HEAP_H_
#define TCMALLOC_PAGE_HEAP_H_

#include <config.h>
#include "common.h"
#include "packed-cache-inl.h"
#include "pagemap.h"
#include "span.h"

// This #ifdef should almost never be set.  Set NO_TCMALLOC_SAMPLES if
// you're porting to a system where you really can't get a stacktrace.
#ifdef NO_TCMALLOC_SAMPLES
  // We use #define so code compiles even if you #include stacktrace.h somehow.
# define GetStackTrace(stack, depth, skip)  (0)
#else
# include <google/stacktrace.h>
#endif

namespace tcmalloc {

// -------------------------------------------------------------------------
// Map from page-id to per-page data
// -------------------------------------------------------------------------

// We use PageMap2<> for 32-bit and PageMap3<> for 64-bit machines.
// ...except...
// On Windows, we use TCMalloc_PageMap1_LazyCommit<> for 32-bit machines.
// We also use a simple one-level cache for hot PageID-to-sizeclass mappings,
// because sometimes the sizeclass is all the information we need.

// Selector class -- general selector uses 3-level map
template <int BITS> class MapSelector {
 public:
  typedef TCMalloc_PageMap3<BITS-kPageShift> Type;
  typedef PackedCache<BITS-kPageShift, uint64_t> CacheType;
};

template <> class MapSelector<32> {
 public:
#ifdef WIN32
// A flat map for 32-bit machines (with lazy commit of memory).
  typedef TCMalloc_PageMap1_LazyCommit<32-kPageShift> Type;
#else
  // A two-level map for 32-bit machines
  typedef TCMalloc_PageMap2<32-kPageShift> Type;
#endif
  typedef PackedCache<32-kPageShift, uint16_t> CacheType;
};

// -------------------------------------------------------------------------
// Page-level allocator
//  * Eager coalescing
//
// Heap for page-level allocation.  We allow allocating and freeing a
// contiguous runs of pages (called a "span").
// -------------------------------------------------------------------------

class PageHeap {
 public:
  PageHeap();

  // Allocate a run of "n" pages.  Returns zero if out of memory.
  // Caller should not pass "n == 0" -- instead, n should have
  // been rounded up already.
  Span* New(Length n);

  // Delete the span "[p, p+n-1]".
  // REQUIRES: span was returned by earlier call to New() and
  //           has not yet been deleted.
  void Delete(Span* span);

  // Mark an allocated span as being used for small objects of the
  // specified size-class.
  // REQUIRES: span was returned by an earlier call to New()
  //           and has not yet been deleted.
  void RegisterSizeClass(Span* span, size_t sc);

  // Split an allocated span into two spans: one of length "n" pages
  // followed by another span of length "span->length - n" pages.
  // Modifies "*span" to point to the first span of length "n" pages.
  // Returns a pointer to the second span.
  //
  // REQUIRES: "0 < n < span->length"
  // REQUIRES: span->location == IN_USE
  // REQUIRES: span->sizeclass == 0
  Span* Split(Span* span, Length n);

  // Return the descriptor for the specified page.
  inline Span* GetDescriptor(PageID p) const {
    return reinterpret_cast<Span*>(pagemap_.get(p));
  }

  // Dump state to stderr
  void Dump(TCMalloc_Printer* out);

  // Return number of bytes allocated from system
  inline uint64_t SystemBytes() const { return system_bytes_; }

  inline uint64_t CommittedBytes() const { return committed_bytes_; }

  // Return number of free bytes in heap
  uint64_t FreeBytes() const {
    return (static_cast<uint64_t>(free_pages_) << kPageShift);
  }

  bool Check();
  // Like Check() but does some more comprehensive checking.
  bool CheckExpensive();
  bool CheckList(Span* list, Length min_pages, Length max_pages,
                 int freelist);  // ON_NORMAL_FREELIST or ON_RETURNED_FREELIST

  // Release all pages on the free list for reuse by the OS:
  void ReleaseFreePages();

  // Return 0 if we have no information, or else the correct sizeclass for p.
  // Reads and writes to pagemap_cache_ do not require locking.
  // The entries are 64 bits on 64-bit hardware and 16 bits on
  // 32-bit hardware, and we don't mind raciness as long as each read of
  // an entry yields a valid entry, not a partially updated entry.
  size_t GetSizeClassIfCached(PageID p) const {
    return pagemap_cache_.GetOrDefault(p, 0);
  }
  void CacheSizeClass(PageID p, size_t cl) const { pagemap_cache_.Put(p, cl); }

 private:
  // Allocates a big block of memory for the pagemap once we reach more than
  // 128MB
  static const size_t kPageMapBigAllocationThreshold = 128 << 20;

  // Minimum number of pages to fetch from system at a time.  Must be
  // significantly bigger than kBlockSize to amortize system-call
  // overhead, and also to reduce external fragementation.  Also, we
  // should keep this value big because various incarnations of Linux
  // have small limits on the number of mmap() regions per
  // address-space.
  static const int kMinSystemAlloc = 1 << (20 - kPageShift);

  // For all span-lengths < kMaxPages we keep an exact-size list.
  // REQUIRED: kMaxPages >= kMinSystemAlloc;
  static const size_t kMaxPages = kMinSystemAlloc;

  // Pick the appropriate map and cache types based on pointer size
  typedef MapSelector<8*sizeof(uintptr_t)>::Type PageMap;
  typedef MapSelector<8*sizeof(uintptr_t)>::CacheType PageMapCache;
  PageMap pagemap_;
  mutable PageMapCache pagemap_cache_;

  // We segregate spans of a given size into two circular linked
  // lists: one for normal spans, and one for spans whose memory
  // has been returned to the system.
  struct SpanList {
    Span        normal;
    Span        returned;
  };

  // List of free spans of length >= kMaxPages
  SpanList large_;

  // Array mapping from span length to a doubly linked list of free spans
  SpanList free_[kMaxPages];

  // Number of pages kept in free lists
  uintptr_t free_pages_;

  // Bytes allocated from system
  uint64_t system_bytes_;

  // Bytes committed, always <= system_bytes_.
  uint64_t committed_bytes_;

  bool GrowHeap(Length n);

  // REQUIRES: span->length >= n
  // REQUIRES: span->location != IN_USE
  // Remove span from its free list, and move any leftover part of
  // span into appropriate free lists.  Also update "span" to have
  // length exactly "n" and mark it as non-free so it can be returned
  // to the client.  After all that, decrease free_pages_ by n and
  // return span.
  Span* Carve(Span* span, Length n);

  void RecordSpan(Span* span) {
    pagemap_.set(span->start, span);
    if (span->length > 1) {
      pagemap_.set(span->start + span->length - 1, span);
    }
  }

  // Allocate a large span of length == n.  If successful, returns a
  // span of exactly the specified length.  Else, returns NULL.
  Span* AllocLarge(Length n);

#if defined(OS_LINUX)
  // Coalesce span with neighboring spans if possible.  Add the
  // resulting span to the appropriate free list.
  void AddToFreeList(Span* span);
#else   // ! defined(OS_LINUX)
  // Commit the span.
  void CommitSpan(Span* span);

  // Decommit the span.
  void DecommitSpan(Span* span);
#endif  // ! defined(OS_LINUX)

  // Incrementally release some memory to the system.
  // IncrementalScavenge(n) is called whenever n pages are freed.
  void IncrementalScavenge(Length n);

#if defined(OS_LINUX)
  // Release all pages in the specified free list for reuse by the OS
  // REQURES: list must be a "normal" list (i.e., not "returned")
  void ReleaseFreeList(Span* list);
#else   // ! defined(OS_LINUX)
  // Releases all memory held in the given list's 'normal' freelist and adds
  // it to the 'released' freelist.
  void ReleaseFreeList(Span* list, Span* returned);
#endif  // ! defined(OS_LINUX)

  // Number of pages to deallocate before doing more scavenging
  int64_t scavenge_counter_;

  // Index of last free list we scavenged
  int scavenge_index_;
};

}  // namespace tcmalloc

#endif  // TCMALLOC_PAGE_HEAP_H_