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[libc] Add a config option to disable slab reclaiming #151599

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[libc] Add a config option to disable slab reclaiming #151599

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12 changes: 8 additions & 4 deletions libc/src/__support/GPU/allocator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,9 @@ constexpr static uint32_t MAX_TRIES = 1024;
// The number of previously allocated slabs we will keep in memory.
constexpr static uint32_t CACHED_SLABS = 8;

// Configuration for whether or not we will return unused slabs to memory.
constexpr static bool RECLAIM = true;

static_assert(!(ARRAY_SIZE & (ARRAY_SIZE - 1)), "Must be a power of two");

namespace impl {
Expand Down Expand Up @@ -399,7 +402,7 @@ struct GuardPtr {
// and obtain exclusive rights to deconstruct it. If the CAS failed either
// another thread resurrected the counter and we quit, or a parallel read
// helped us invalidating it. For the latter, claim that flag and return.
if (counter.fetch_sub(n, cpp::MemoryOrder::RELAXED) == n) {
if (counter.fetch_sub(n, cpp::MemoryOrder::RELAXED) == n && RECLAIM) {
uint32_t expected = 0;
if (counter.compare_exchange_strong(expected, INVALID,
cpp::MemoryOrder::RELAXED,
Expand All @@ -417,8 +420,9 @@ struct GuardPtr {
// thread.
uint64_t read() {
auto val = counter.load(cpp::MemoryOrder::RELAXED);
if (val == 0 && counter.compare_exchange_strong(
val, INVALID | HELPED, cpp::MemoryOrder::RELAXED))
if (val == 0 && RECLAIM &&
counter.compare_exchange_strong(val, INVALID | HELPED,
cpp::MemoryOrder::RELAXED))
return 0;
return (val & INVALID) ? 0 : val;
}
Expand Down Expand Up @@ -463,7 +467,7 @@ struct GuardPtr {
return nullptr;

cpp::atomic_thread_fence(cpp::MemoryOrder::ACQUIRE);
return ptr.load(cpp::MemoryOrder::RELAXED);
return RECLAIM ? ptr.load(cpp::MemoryOrder::RELAXED) : expected;
}

// Finalize the associated memory and signal that it is ready to use by
Expand Down
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