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Background house-keeping & pre-existing thread
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Break apart ProcessBackgroundActions into an "Init" and "Tick" stage and
leave periodic invocation to the caller. This lets users reduce
the number of threads spun up by 1 if they already have a background
house keeping thread that knows when (& perhaps even how much) memory to
free.
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vlovich committed Aug 25, 2021
1 parent 5d35433 commit c4892ca
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Showing 4 changed files with 67 additions and 25 deletions.
61 changes: 36 additions & 25 deletions tcmalloc/background.cc
Original file line number Diff line number Diff line change
Expand Up @@ -99,43 +99,54 @@ void ShuffleCpuCaches() {
GOOGLE_MALLOC_SECTION_END

// Release memory to the system at a constant rate.
void MallocExtension_Internal_ProcessBackgroundActions() {
tcmalloc::MallocExtension::MarkThreadIdle();
static absl::Time prev_time;
static absl::Time last_shuffle;

void MallocExtension_Internal_ProcessBackgroundActionsInit() {
// Initialize storage for ReleasePerCpuMemoryToOS().
CPU_ZERO(&tcmalloc::tcmalloc_internal::prev_allowed_cpus);

absl::Time prev_time = absl::Now();
prev_time = absl::Now();
last_shuffle = absl::InfinitePast();
}

void MallocExtension_Internal_ProcessBackgroundActions() {
constexpr absl::Duration kSleepTime = absl::Seconds(1);

tcmalloc::MallocExtension::MarkThreadIdle();
MallocExtension_Internal_ProcessBackgroundActionsInit();

while (true) {
MallocExtension_Internal_ProcessBackgroundActionsTick();
absl::SleepFor(kSleepTime);
}
}

void MallocExtension_Internal_ProcessBackgroundActionsTick() {
// Shuffle per-cpu caches once per kCpuCacheShufflePeriod secs.
constexpr absl::Duration kCpuCacheShufflePeriod = absl::Seconds(5);
absl::Time last_shuffle = absl::InfinitePast();

while (true) {
absl::Time now = absl::Now();
const ssize_t bytes_to_release =
static_cast<size_t>(tcmalloc::tcmalloc_internal::Parameters::
background_release_rate()) *
absl::ToDoubleSeconds(now - prev_time);
if (bytes_to_release > 0) { // may be negative if time goes backwards
tcmalloc::MallocExtension::ReleaseMemoryToSystem(bytes_to_release);
}
absl::Time now = absl::Now();
const ssize_t bytes_to_release =
static_cast<size_t>(tcmalloc::tcmalloc_internal::Parameters::
background_release_rate()) *
absl::ToDoubleSeconds(now - prev_time);
if (bytes_to_release > 0) { // may be negative if time goes backwards
tcmalloc::MallocExtension::ReleaseMemoryToSystem(bytes_to_release);
}

tcmalloc::tcmalloc_internal::ReleasePerCpuMemoryToOS();
tcmalloc::tcmalloc_internal::ReleasePerCpuMemoryToOS();

const bool shuffle_per_cpu_caches =
tcmalloc::tcmalloc_internal::Parameters::shuffle_per_cpu_caches();
const bool shuffle_per_cpu_caches =
tcmalloc::tcmalloc_internal::Parameters::shuffle_per_cpu_caches();

if (shuffle_per_cpu_caches) {
if (now - last_shuffle >= kCpuCacheShufflePeriod) {
tcmalloc::tcmalloc_internal::ShuffleCpuCaches();
last_shuffle = now;
}
if (shuffle_per_cpu_caches) {
if (now - last_shuffle >= kCpuCacheShufflePeriod) {
tcmalloc::tcmalloc_internal::ShuffleCpuCaches();
last_shuffle = now;
}

tcmalloc::tcmalloc_internal::Static().sharded_transfer_cache().Plunder();
prev_time = now;
absl::SleepFor(kSleepTime);
}

tcmalloc::tcmalloc_internal::Static().sharded_transfer_cache().Plunder();
prev_time = now;
}
2 changes: 2 additions & 0 deletions tcmalloc/internal_malloc_extension.h
Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,8 @@ ABSL_ATTRIBUTE_WEAK void MallocExtension_Internal_SetProfileSamplingRate(
int64_t);

ABSL_ATTRIBUTE_WEAK void MallocExtension_Internal_ProcessBackgroundActions();
ABSL_ATTRIBUTE_WEAK void MallocExtension_Internal_ProcessBackgroundActionsInit();
ABSL_ATTRIBUTE_WEAK void MallocExtension_Internal_ProcessBackgroundActionsTick();

ABSL_ATTRIBUTE_WEAK tcmalloc::MallocExtension::BytesPerSecond
MallocExtension_Internal_GetBackgroundReleaseRate();
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16 changes: 16 additions & 0 deletions tcmalloc/malloc_extension.cc
Original file line number Diff line number Diff line change
Expand Up @@ -425,6 +425,22 @@ void MallocExtension::ProcessBackgroundActions() {
#endif
}

void MallocExtension::ProcessBackgroundActionsInit() {
#if ABSL_INTERNAL_HAVE_WEAK_MALLOCEXTENSION_STUBS
if (NeedsProcessBackgroundActions()) {
MallocExtension_Internal_ProcessBackgroundActionsInit();
}
#endif
}

void MallocExtension::ProcessBackgroundActionsTick() {
#if ABSL_INTERNAL_HAVE_WEAK_MALLOCEXTENSION_STUBS
if (NeedsProcessBackgroundActions()) {
MallocExtension_Internal_ProcessBackgroundActionsTick();
}
#endif
}

bool MallocExtension::NeedsProcessBackgroundActions() {
#if ABSL_INTERNAL_HAVE_WEAK_MALLOCEXTENSION_STUBS
return &MallocExtension_Internal_ProcessBackgroundActions != nullptr;
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13 changes: 13 additions & 0 deletions tcmalloc/malloc_extension.h
Original file line number Diff line number Diff line change
Expand Up @@ -433,6 +433,19 @@ class MallocExtension final {
// null if the implementation does not support profiling.
static AllocationProfilingToken StartAllocationProfiling();

// Initializes the state needed for this thread to call
// ProcessBackgroundActionsTick. This is the counterpart to
// ProcessBackgroundActions that allows co-operative task keeping on a thread
// that is performing other task keeping.
static void ProcessBackgroundActionsInit();

// This is to be called periodically to run housekeeping actions for the
// allocator off of the main allocation paths of new/delete. Note that unlike
// ProcessBackgroundActions, the thread is not automatically marked as
// idle/busy and the caller is responsible for doing that correctly.
// See ProcessBackgroundActions for details of the actions performed.
static void ProcessBackgroundActionsTick();

// Runs housekeeping actions for the allocator off of the main allocation path
// of new/delete. As of 2020, this includes:
// * Inspecting the current CPU mask and releasing memory from inaccessible
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