HeapSizeHistogram.h File Reference

Live-heap histogram by allocation size (the single-canvas presenter work investigation). More...

#include <cstddef>
#include <cstdint>

Include dependency graph for HeapSizeHistogram.h:

This graph shows which files directly or indirectly include this file:

Classes
struct	donner::AllocTagTotals
	Live large-block bytes attributed to each AllocTag. More...
class	donner::ScopedAllocTag
	Sets the calling thread's AllocTag for the lifetime of the scope, restoring the previous one on exit so guards nest. More...
struct	donner::HeapSizeHistogram
	Live allocation totals split by block size. More...

Namespaces
namespace	donner
	Top-level Donner namespace, which is split into different sub-namespaces such as donner::svg and donner::css.

Enumerations
enum class	donner::AllocTag : std::uint8_t {   donner::Untagged = 0 ,   donner::WorkerRenderFrame = 1 ,   donner::WorkerBuildPreview = 2 ,   donner::WorkerFinalSnapshot = 3 ,   donner::WorkerOther = 4 ,   donner::AppPollResult = 5 ,   donner::AppUiFrame = 6 ,   donner::AppHostFrame = 7 ,   donner::AppInput = 8 ,   donner::RenderTileRaster = 9 ,   donner::GpuReadbackStaging = 10 ,   donner::CompositorBitmap = 11 ,   donner::PresentationUpload = 12 ,   donner::ImGuiDrawLists = 13 }
	Who was on the stack when a large block was allocated. More...

Functions
const char *	donner::AllocTagName (AllocTag tag)
	Stable short names for AllocTag, indexed by the enum value.
AllocTagTotals	donner::SampleAllocTagTotals ()
	Read the per-tag live large-block totals.
HeapSizeHistogram	donner::SampleHeapSizeHistogram ()
	Read the histogram. Cheap: a load per bucket.
bool	donner::HeapSizeHistogramEnabled ()
	Whether the allocator wrappers are linked in. False in shipping builds.

Variables
constexpr std::size_t	donner::kHeapSizeBucketCount = 32
	Number of power-of-two size buckets. Bucket k covers [2^k, 2^(k+1)) bytes, so 32 buckets reach 2 GiB, past anything a 512 MiB wasm heap can hold.
constexpr std::size_t	donner::kLargeAllocationBytes = 4u * 1024u * 1024u
	Requested byte size at or above which an allocation is recorded in HeapSizeHistogram::recentLargeBytes. Chosen to catch anything canvas-scale while ignoring ordinary containers.
constexpr std::size_t	donner::kRecentLargeAllocationCount = 16
	Number of recent large allocation sizes retained.
constexpr std::size_t	donner::kLiveLargeBlockCount = 48
	Capacity of the live large-block table.
constexpr std::size_t	donner::kAllocTagCount = 14
	Number of distinct AllocTag values.

Detailed Description

Live-heap histogram by allocation size (the single-canvas presenter work investigation).

See HeapSizeHistogram.cc for what this measures and how to turn it on. The header compiles and the accessors link in every configuration; without DONNER_HEAP_SIZE_HISTOGRAM they report an empty histogram and HeapSizeHistogramEnabled returns false, so callers never need their own preprocessor guard.

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Class Documentation

donner::AllocTagTotals

struct donner::AllocTagTotals

Live large-block bytes attributed to each AllocTag.

Class Members
int64_t	liveBlocks[kAllocTagCount] = {}	Live large blocks tagged with this value.
int64_t	liveBytes[kAllocTagCount] = {}	Bytes in live large blocks tagged with this value.
int64_t	peakLiveBytes[kAllocTagCount] = {}	Highest liveBytes seen for this tag.
int64_t	totalAllocations[kAllocTagCount] = {}	Large allocations ever made under this tag.

donner::HeapSizeHistogram

struct donner::HeapSizeHistogram

Live allocation totals split by block size.

Class Members
int64_t	largeAllocationCount = 0	Total large allocations seen since boot.
int64_t	liveBlocks[kHeapSizeBucketCount] = {}	Currently allocated block count in each bucket.
int64_t	liveBytes[kHeapSizeBucketCount] = {}	Currently allocated bytes in each bucket, measured as usable size.
int64_t	liveLargeBytes[kLiveLargeBlockCount] = {}	Usable sizes of the large blocks that are live right now; zero entries are empty slots.
int64_t	liveLargeTags[kLiveLargeBlockCount] = {}	AllocTag in force when the corresponding liveLargeBytes entry was allocated, as its integer value.
int64_t	peakLiveBytes[kHeapSizeBucketCount] = {}	Highest liveBytes seen in each bucket.
int64_t	recentLargeBytes[kRecentLargeAllocationCount] = {}	Requested sizes of the most recent large allocations, newest last. A bucket says a block is "16 to 32 MiB"; this says it is exactly 19,120,128 bytes, which is a 2186-pixel-wide RGBA surface and therefore identifies its owner by arithmetic instead of by guesswork.
int64_t	tableOverflows = 0	Large allocations that found the live-block table full. Non-zero means the per-tag totals under-count and kLiveLargeBlockCount needs raising.