release.h

//===-- release.h -----------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef SCUDO_RELEASE_H_
#define SCUDO_RELEASE_H_

#include "common.h"
#include "list.h"
#include "mutex.h"

namespace scudo {

class ReleaseRecorder {
public:
  ReleaseRecorder(uptr Base, MapPlatformData *Data = nullptr)
      : Base(Base), Data(Data) {}

  uptr getReleasedRangesCount() const { return ReleasedRangesCount; }

  uptr getReleasedBytes() const { return ReleasedBytes; }

  uptr getBase() const { return Base; }

  // Releases [From, To) range of pages back to OS.
  void releasePageRangeToOS(uptr From, uptr To) {
    const uptr Size = To - From;
    releasePagesToOS(Base, From, Size, Data);
    ReleasedRangesCount++;
    ReleasedBytes += Size;
  }

private:
  uptr ReleasedRangesCount = 0;
  uptr ReleasedBytes = 0;
  uptr Base = 0;
  MapPlatformData *Data = nullptr;
};

// A packed array of Counters. Each counter occupies 2^N bits, enough to store
// counter's MaxValue. Ctor will try to use a static buffer first, and if that
// fails (the buffer is too small or already locked), will allocate the
// required Buffer via map(). The caller is expected to check whether the
// initialization was successful by checking isAllocated() result. For
// performance sake, none of the accessors check the validity of the arguments,
// It is assumed that Index is always in [0, N) range and the value is not
// incremented past MaxValue.
class PackedCounterArray {
public:
  PackedCounterArray(uptr NumberOfRegions, uptr CountersPerRegion,
                     uptr MaxValue)
      : Regions(NumberOfRegions), NumCounters(CountersPerRegion) {
    DCHECK_GT(Regions, 0);
    DCHECK_GT(NumCounters, 0);
    DCHECK_GT(MaxValue, 0);
    constexpr uptr MaxCounterBits = sizeof(*Buffer) * 8UL;
    // Rounding counter storage size up to the power of two allows for using
    // bit shifts calculating particular counter's Index and offset.
    const uptr CounterSizeBits =
        roundUpToPowerOfTwo(getMostSignificantSetBitIndex(MaxValue) + 1);
    DCHECK_LE(CounterSizeBits, MaxCounterBits);
    CounterSizeBitsLog = getLog2(CounterSizeBits);
    CounterMask = ~(static_cast<uptr>(0)) >> (MaxCounterBits - CounterSizeBits);

    const uptr PackingRatio = MaxCounterBits >> CounterSizeBitsLog;
    DCHECK_GT(PackingRatio, 0);
    PackingRatioLog = getLog2(PackingRatio);
    BitOffsetMask = PackingRatio - 1;

    SizePerRegion =
        roundUpTo(NumCounters, static_cast<uptr>(1U) << PackingRatioLog) >>
        PackingRatioLog;
    BufferSize = SizePerRegion * sizeof(*Buffer) * Regions;
    if (BufferSize <= (StaticBufferCount * sizeof(Buffer[0])) &&
        Mutex.tryLock()) {
      Buffer = &StaticBuffer[0];
      memset(Buffer, 0, BufferSize);
    } else {
      Buffer = reinterpret_cast<uptr *>(
          map(nullptr, BufferSize, "scudo:counters", MAP_ALLOWNOMEM));
    }
  }
  ~PackedCounterArray() {
    if (!isAllocated())
      return;
    if (Buffer == &StaticBuffer[0])
      Mutex.unlock();
    else
      unmap(reinterpret_cast<void *>(Buffer), BufferSize);
  }

  bool isAllocated() const { return !!Buffer; }

  uptr getCount() const { return NumCounters; }

  uptr get(uptr Region, uptr I) const {
    DCHECK_LT(Region, Regions);
    DCHECK_LT(I, NumCounters);
    const uptr Index = I >> PackingRatioLog;
    const uptr BitOffset = (I & BitOffsetMask) << CounterSizeBitsLog;
    return (Buffer[Region * SizePerRegion + Index] >> BitOffset) & CounterMask;
  }

  void inc(uptr Region, uptr I) const {
    DCHECK_LT(get(Region, I), CounterMask);
    const uptr Index = I >> PackingRatioLog;
    const uptr BitOffset = (I & BitOffsetMask) << CounterSizeBitsLog;
    DCHECK_LT(BitOffset, SCUDO_WORDSIZE);
    Buffer[Region * SizePerRegion + Index] += static_cast<uptr>(1U)
                                              << BitOffset;
  }

  void incRange(uptr Region, uptr From, uptr To) const {
    DCHECK_LE(From, To);
    const uptr Top = Min(To + 1, NumCounters);
    for (uptr I = From; I < Top; I++)
      inc(Region, I);
  }

  uptr getBufferSize() const { return BufferSize; }

  static const uptr StaticBufferCount = 2048U;

private:
  const uptr Regions;
  const uptr NumCounters;
  uptr CounterSizeBitsLog;
  uptr CounterMask;
  uptr PackingRatioLog;
  uptr BitOffsetMask;

  uptr SizePerRegion;
  uptr BufferSize;
  uptr *Buffer;

  static HybridMutex Mutex;
  static uptr StaticBuffer[StaticBufferCount];
};

template <class ReleaseRecorderT> class FreePagesRangeTracker {
public:
  explicit FreePagesRangeTracker(ReleaseRecorderT *Recorder)
      : Recorder(Recorder), PageSizeLog(getLog2(getPageSizeCached())) {}

  void processNextPage(bool Freed) {
    if (Freed) {
      if (!InRange) {
        CurrentRangeStatePage = CurrentPage;
        InRange = true;
      }
    } else {
      closeOpenedRange();
    }
    CurrentPage++;
  }

  void skipPages(uptr N) {
    closeOpenedRange();
    CurrentPage += N;
  }

  void finish() { closeOpenedRange(); }

private:
  void closeOpenedRange() {
    if (InRange) {
      Recorder->releasePageRangeToOS((CurrentRangeStatePage << PageSizeLog),
                                     (CurrentPage << PageSizeLog));
      InRange = false;
    }
  }

  ReleaseRecorderT *const Recorder;
  const uptr PageSizeLog;
  bool InRange = false;
  uptr CurrentPage = 0;
  uptr CurrentRangeStatePage = 0;
};

template <class TransferBatchT, class ReleaseRecorderT, typename DecompactPtrT,
          typename SkipRegionT>
NOINLINE void
releaseFreeMemoryToOS(const IntrusiveList<TransferBatchT> &FreeList,
                      uptr RegionSize, uptr NumberOfRegions, uptr BlockSize,
                      ReleaseRecorderT *Recorder, DecompactPtrT DecompactPtr,
                      SkipRegionT SkipRegion) {
  const uptr PageSize = getPageSizeCached();

  // Figure out the number of chunks per page and whether we can take a fast
  // path (the number of chunks per page is the same for all pages).
  uptr FullPagesBlockCountMax;
  bool SameBlockCountPerPage;
  if (BlockSize <= PageSize) {
    if (PageSize % BlockSize == 0) {
      // Same number of chunks per page, no cross overs.
      FullPagesBlockCountMax = PageSize / BlockSize;
      SameBlockCountPerPage = true;
    } else if (BlockSize % (PageSize % BlockSize) == 0) {
      // Some chunks are crossing page boundaries, which means that the page
      // contains one or two partial chunks, but all pages contain the same
      // number of chunks.
      FullPagesBlockCountMax = PageSize / BlockSize + 1;
      SameBlockCountPerPage = true;
    } else {
      // Some chunks are crossing page boundaries, which means that the page
      // contains one or two partial chunks.
      FullPagesBlockCountMax = PageSize / BlockSize + 2;
      SameBlockCountPerPage = false;
    }
  } else {
    if (BlockSize % PageSize == 0) {
      // One chunk covers multiple pages, no cross overs.
      FullPagesBlockCountMax = 1;
      SameBlockCountPerPage = true;
    } else {
      // One chunk covers multiple pages, Some chunks are crossing page
      // boundaries. Some pages contain one chunk, some contain two.
      FullPagesBlockCountMax = 2;
      SameBlockCountPerPage = false;
    }
  }

  const uptr PagesCount = roundUpTo(RegionSize, PageSize) / PageSize;
  PackedCounterArray Counters(NumberOfRegions, PagesCount,
                              FullPagesBlockCountMax);
  if (!Counters.isAllocated())
    return;

  const uptr PageSizeLog = getLog2(PageSize);
  const uptr RoundedRegionSize = PagesCount << PageSizeLog;
  const uptr RoundedSize = NumberOfRegions * RoundedRegionSize;

  // Iterate over free chunks and count how many free chunks affect each
  // allocated page.
  if (BlockSize <= PageSize && PageSize % BlockSize == 0) {
    // Each chunk affects one page only.
    for (const auto &It : FreeList) {
      for (u32 I = 0; I < It.getCount(); I++) {
        const uptr P = DecompactPtr(It.get(I)) - Recorder->getBase();
        if (P >= RoundedSize)
          continue;
        const uptr RegionIndex = NumberOfRegions == 1U ? 0 : P / RegionSize;
        const uptr PInRegion = P - RegionIndex * RegionSize;
        Counters.inc(RegionIndex, PInRegion >> PageSizeLog);
      }
    }
  } else {
    // In all other cases chunks might affect more than one page.
    DCHECK_GE(RegionSize, BlockSize);
    const uptr LastBlockInRegion = ((RegionSize / BlockSize) - 1U) * BlockSize;
    for (const auto &It : FreeList) {
      for (u32 I = 0; I < It.getCount(); I++) {
        const uptr P = DecompactPtr(It.get(I)) - Recorder->getBase();
        if (P >= RoundedSize)
          continue;
        const uptr RegionIndex = NumberOfRegions == 1U ? 0 : P / RegionSize;
        uptr PInRegion = P - RegionIndex * RegionSize;
        Counters.incRange(RegionIndex, PInRegion >> PageSizeLog,
                          (PInRegion + BlockSize - 1) >> PageSizeLog);
        // The last block in a region might straddle a page, so if it's
        // free, we mark the following "pretend" memory block(s) as free.
        if (PInRegion == LastBlockInRegion) {
          PInRegion += BlockSize;
          while (PInRegion < RoundedRegionSize) {
            Counters.incRange(RegionIndex, PInRegion >> PageSizeLog,
                              (PInRegion + BlockSize - 1) >> PageSizeLog);
            PInRegion += BlockSize;
          }
        }
      }
    }
  }

  // Iterate over pages detecting ranges of pages with chunk Counters equal
  // to the expected number of chunks for the particular page.
  FreePagesRangeTracker<ReleaseRecorderT> RangeTracker(Recorder);
  if (SameBlockCountPerPage) {
    // Fast path, every page has the same number of chunks affecting it.
    for (uptr I = 0; I < NumberOfRegions; I++) {
      if (SkipRegion(I)) {
        RangeTracker.skipPages(PagesCount);
        continue;
      }
      for (uptr J = 0; J < PagesCount; J++)
        RangeTracker.processNextPage(Counters.get(I, J) ==
                                     FullPagesBlockCountMax);
    }
  } else {
    // Slow path, go through the pages keeping count how many chunks affect
    // each page.
    const uptr Pn = BlockSize < PageSize ? PageSize / BlockSize : 1;
    const uptr Pnc = Pn * BlockSize;
    // The idea is to increment the current page pointer by the first chunk
    // size, middle portion size (the portion of the page covered by chunks
    // except the first and the last one) and then the last chunk size, adding
    // up the number of chunks on the current page and checking on every step
    // whether the page boundary was crossed.
    for (uptr I = 0; I < NumberOfRegions; I++) {
      if (SkipRegion(I)) {
        RangeTracker.skipPages(PagesCount);
        continue;
      }
      uptr PrevPageBoundary = 0;
      uptr CurrentBoundary = 0;
      for (uptr J = 0; J < PagesCount; J++) {
        const uptr PageBoundary = PrevPageBoundary + PageSize;
        uptr BlocksPerPage = Pn;
        if (CurrentBoundary < PageBoundary) {
          if (CurrentBoundary > PrevPageBoundary)
            BlocksPerPage++;
          CurrentBoundary += Pnc;
          if (CurrentBoundary < PageBoundary) {
            BlocksPerPage++;
            CurrentBoundary += BlockSize;
          }
        }
        PrevPageBoundary = PageBoundary;
        RangeTracker.processNextPage(Counters.get(I, J) == BlocksPerPage);
      }
    }
  }
  RangeTracker.finish();
}

} // namespace scudo

#endif // SCUDO_RELEASE_H_