1 // Copyright 2019 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #include "base/profiler/stack_buffer.h"
8 #if BUILDFLAG(IS_CHROMEOS)
13 #include "base/check.h"
14 #include "base/check_op.h"
15 #include "base/memory/page_size.h"
16 #endif // #if BUILDFLAG(IS_CHROMEOS)
20 constexpr size_t StackBuffer::kPlatformStackAlignment;
22 #if BUILDFLAG(IS_CHROMEOS)
24 void StackBuffer::MarkUpperBufferContentsAsUnneeded(size_t retained_bytes) {
25 // Round up to the next multiple of the page size. madvise needs the
26 // starting address to be page aligned. Since buffer_.get() is
27 // already page aligned, we just need to round up the retained bytes.
28 size_t actual_retained_bytes = bits::AlignUp(retained_bytes, GetPageSize());
30 // Avoid passing a negative discard_size to madvise(). Doing so would randomly
31 // discard large amounts of memory causing weird crashes.
32 CHECK_LE(actual_retained_bytes, size_);
34 uint8_t* start_of_discard =
35 reinterpret_cast<uint8_t*>(buffer_.get()) + actual_retained_bytes;
36 size_t discard_size = size_ - actual_retained_bytes;
37 int result = madvise(start_of_discard, discard_size, MADV_DONTNEED);
39 DPCHECK(result == 0) << "madvise failed: ";
42 #endif // #if BUILDFLAG(IS_CHROMEOS)
44 StackBuffer::StackBuffer(size_t buffer_size)
45 #if BUILDFLAG(IS_CHROMEOS)
46 // On ChromeOS, we have 8MB of stack space per thread; however, we normally
47 // only use a small fraction of that. To avoid blowing our memory budget,
48 // we use madvise(MADV_DONTNEED) to let the kernel discard the memory in the
49 // 8MB buffer except when we are actively using it. For madvise() to work,
50 // we need |buffer_| to be aligned to a page boundary.
52 // We also need the |size_| to be a multiple of the page size so that we
53 // don't pass partial pages to madvise(). This isn't documented but the
54 // program will consistently crash otherwise.
55 : size_(bits::AlignUp(buffer_size, GetPageSize())),
56 buffer_(static_cast<uintptr_t*>(AlignedAlloc(size_, GetPageSize()))) {
57 // Our (very large) buffer may already have data written to it & thus have
58 // backing pages. Tell the kernel we don't need the current contents.
59 MarkUpperBufferContentsAsUnneeded(0);
61 #else // #if BUILDFLAG(IS_CHROMEOS)
63 buffer_(static_cast<uintptr_t*>(
64 AlignedAlloc(size_, kPlatformStackAlignment))) {
65 static_assert(bits::IsPowerOfTwo(kPlatformStackAlignment));
67 #endif // !#if BUILDFLAG(IS_CHROMEOS)
69 StackBuffer::~StackBuffer() = default;