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Strength-reduce per-span division in CentralFreeList::DeallocateSpans. #725

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copybara-service merged 1 commit into from
Sep 12, 2026
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Strength-reduce per-span division in CentralFreeList::DeallocateSpans. #725

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10 changes: 10 additions & 0 deletions tcmalloc/central_freelist.h
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Original file line number Diff line number Diff line change
Expand Up @@ -671,11 +671,21 @@ void CentralFreeList<Forwarder>::DeallocateSpans(absl::Span<Span*> spans) {
if (objects_per_span_ > 1) {
const double now = forwarder_.clock_now();
const double frequency = forwarder_.clock_frequency();
#ifndef TCMALLOC_INTERNAL_LEGACY_LOCKING
// Precompute the cycles->milliseconds factor once so the per-span
// conversion is a multiply instead of a floating-point division.
const double ms_per_cycle = 1000.0 / frequency;
#endif
for (Span* span : spans) {
const double elapsed =
std::max<double>(now - static_cast<double>(span->AllocTime()), 0.0);
#ifdef TCMALLOC_INTERNAL_LEGACY_LOCKING
const absl::Duration lifetime =
absl::Milliseconds(elapsed * 1000 / frequency);
#else
const absl::Duration lifetime =
absl::Milliseconds(elapsed * ms_per_cycle);
#endif
completed_spans_[LifetimeBucketNum(lifetime)].LossyAdd(1);
}
}
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