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Restrict pre-fetching to smaller heaps. #345

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May 23, 2022
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Restrict pre-fetching to smaller heaps. #345

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18 changes: 14 additions & 4 deletions src/gpgmm/common/SlabMemoryAllocator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,9 +23,19 @@

namespace gpgmm {

constexpr static uint64_t kSlabPrefetchTotalBlockCount = 4u;
// Disables pre-fetching of memory objects that have too little space.
constexpr static uint64_t kSlabPrefetchMinBlockCount = 4u;

// Disables pre-fetching of memory objects that are under-utilizied.
constexpr static double kSlabPrefetchUsageThreshold = 0.50;

// Disables pre-fetching of memory objects that are too large.
// Larger memory objects require more time on the device to allocate memory and could block a
// subsequent allocation request using a previously allocated memory object. This threshold
// is used to restrict pre-fetching to smaller memory blocks to ensure the application is busy
// and not waiting on the next pre-fetched allocation.
constexpr static uint64_t kSlabPrefetchMemorySizeThreshold = 64 * 1024 * 1024;

// SlabMemoryAllocator

SlabMemoryAllocator::SlabMemoryAllocator(uint64_t blockSize,
Expand Down Expand Up @@ -223,15 +233,15 @@ namespace gpgmm {
if ((request.AlwaysPrefetch || mAllowSlabPrefetch) && !request.NeverAllocate &&
mNextSlabAllocationEvent == nullptr &&
pFreeSlab->GetUsedPercent() >= kSlabPrefetchUsageThreshold &&
pFreeSlab->GetBlockCount() >= kSlabPrefetchTotalBlockCount) {
pFreeSlab->GetBlockCount() >= kSlabPrefetchMinBlockCount) {
// If a subsequent TryAllocateMemory() uses a request size different than the current
// request size, memory required for the next slab could be the wrong size. If so,
// pre-fetching did not pay off and the pre-fetched memory will be de-allocated instead.
const uint64_t nextSlabSize = std::min(
ComputeSlabSize(request.SizeInBytes, mLastUsedSlabSize * mSlabGrowthFactor),
mMaxSlabSize);

if (nextSlabSize < request.AvailableForAllocation) {
if (nextSlabSize < request.AvailableForAllocation &&
nextSlabSize <= kSlabPrefetchMemorySizeThreshold) {
MEMORY_ALLOCATION_REQUEST newSlabRequest = request;
newSlabRequest.SizeInBytes = nextSlabSize;
newSlabRequest.Alignment = mSlabAlignment;
Expand Down