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- // Copyright 2019 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.
- #include "base/profiler/stack_buffer.h"
- #include "base/bits.h"
- #if BUILDFLAG(IS_CHROMEOS)
- #include <sys/mman.h>
- #include <ostream>
- #include "base/check.h"
- #include "base/check_op.h"
- #include "base/memory/page_size.h"
- #endif // #if BUILDFLAG(IS_CHROMEOS)
- namespace base {
- constexpr size_t StackBuffer::kPlatformStackAlignment;
- #if BUILDFLAG(IS_CHROMEOS)
- void StackBuffer::MarkUpperBufferContentsAsUnneeded(size_t retained_bytes) {
- // Round up to the next multiple of the page size. madvise needs the
- // starting address to be page aligned. Since buffer_.get() is
- // already page aligned, we just need to round up the retained bytes.
- size_t actual_retained_bytes = bits::AlignUp(retained_bytes, GetPageSize());
- // Avoid passing a negative discard_size to madvise(). Doing so would randomly
- // discard large amounts of memory causing weird crashes.
- CHECK_LE(actual_retained_bytes, size_);
- uint8_t* start_of_discard =
- reinterpret_cast<uint8_t*>(buffer_.get()) + actual_retained_bytes;
- size_t discard_size = size_ - actual_retained_bytes;
- int result = madvise(start_of_discard, discard_size, MADV_DONTNEED);
- DPCHECK(result == 0) << "madvise failed: ";
- }
- #endif // #if BUILDFLAG(IS_CHROMEOS)
- StackBuffer::StackBuffer(size_t buffer_size)
- #if BUILDFLAG(IS_CHROMEOS)
- // On ChromeOS, we have 8MB of stack space per thread; however, we normally
- // only use a small fraction of that. To avoid blowing our memory budget,
- // we use madvise(MADV_DONTNEED) to let the kernel discard the memory in the
- // 8MB buffer except when we are actively using it. For madvise() to work,
- // we need |buffer_| to be aligned to a page boundary.
- //
- // We also need the |size_| to be a multiple of the page size so that we
- // don't pass partial pages to madvise(). This isn't documented but the
- // program will consistently crash otherwise.
- : size_(bits::AlignUp(buffer_size, GetPageSize())),
- buffer_(static_cast<uintptr_t*>(AlignedAlloc(size_, GetPageSize()))) {
- // Our (very large) buffer may already have data written to it & thus have
- // backing pages. Tell the kernel we don't need the current contents.
- MarkUpperBufferContentsAsUnneeded(0);
- }
- #else // #if BUILDFLAG(IS_CHROMEOS)
- : size_(buffer_size),
- buffer_(static_cast<uintptr_t*>(
- AlignedAlloc(size_, kPlatformStackAlignment))) {
- static_assert(bits::IsPowerOfTwo(kPlatformStackAlignment));
- }
- #endif // !#if BUILDFLAG(IS_CHROMEOS)
- StackBuffer::~StackBuffer() = default;
- } // namespace base
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