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Fix off-by-one in stacktrace filter probability when pool is empty. #293

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Fix off-by-one in stacktrace filter probability when pool is empty. #293

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be6d592
Fix off-by-one in stacktrace filter probability when pool is empty.
cuiweixie Mar 18, 2026
0bdf87a
fix: review
cuiweixie Mar 18, 2026
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4 changes: 2 additions & 2 deletions tcmalloc/guarded_page_allocator.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -143,10 +143,10 @@ GuardedAllocWithStatus GuardedPageAllocator::TrySample(

if (stacktrace_filter_.Contains({stack_trace.stack, stack_trace.depth})) {
// The probability that we skip a currently covered allocation scales
// proportional to pool utilization, with pool utilization of 50% or more
// proportional to pool utilization, with pool utilization greater than 50%
// resulting in always filtering currently covered allocations.
const size_t usage_pct = (allocated_pages() * 100) / max_allocated_pages_;
if (rand_.Next() % 50 <= usage_pct) {
if (rand_.Next() % 50 < usage_pct) {
// Decay even if the current allocation is filtered, so that we keep
// sampling even if we only see the same allocations over and over.
stacktrace_filter_.Decay();
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