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LocalAllocator: add alloc_hinted #487

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LocalAllocator: add alloc_hinted #487

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55 changes: 43 additions & 12 deletions src/mem/localalloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -167,7 +167,7 @@ namespace snmalloc
* passed to the core allocator.
*/
template<ZeroMem zero_mem>
SNMALLOC_SLOW_PATH capptr::Alloc<void> alloc_not_small(size_t size)
SNMALLOC_FAST_PATH capptr::Alloc<void> alloc_not_small_fast(size_t size)
{
if (size == 0)
{
Expand Down Expand Up @@ -206,6 +206,12 @@ namespace snmalloc
});
}

template<ZeroMem zero_mem>
SNMALLOC_SLOW_PATH capptr::Alloc<void> alloc_not_small(size_t size)
{
return alloc_not_small_fast<zero_mem>(size);
}

template<ZeroMem zero_mem>
SNMALLOC_FAST_PATH capptr::Alloc<void> small_alloc(size_t size)
{
Expand Down Expand Up @@ -241,6 +247,12 @@ namespace snmalloc
domesticate, size, slowpath);
}

template<ZeroMem zero_mem>
SNMALLOC_SLOW_PATH capptr::Alloc<void> small_alloc_slow(size_t size)
{
return small_alloc<zero_mem>(size);
}

/**
* Send all remote deallocation to other threads.
*/
Expand Down Expand Up @@ -416,8 +428,8 @@ namespace snmalloc
/**
* Allocate memory of a dynamically known size.
*/
template<ZeroMem zero_mem = NoZero>
SNMALLOC_FAST_PATH ALLOCATOR void* alloc(size_t size)
template<size_t size_hint, ZeroMem zero_mem = NoZero>
SNMALLOC_FAST_PATH ALLOCATOR void* alloc_hinted(size_t size)
{
#ifdef SNMALLOC_PASS_THROUGH
// snmalloc guarantees a lot of alignment, so we can depend on this
Expand All @@ -429,27 +441,46 @@ namespace snmalloc
memset(result, 0, size);
return result;
#else
// Perform the - 1 on size, so that zero wraps around and ends up on
// slow path.
if (SNMALLOC_LIKELY(
(size - 1) <= (sizeclass_to_size(NUM_SMALL_SIZECLASSES - 1) - 1)))
if constexpr (
(size_hint - 1) <= (sizeclass_to_size(NUM_SMALL_SIZECLASSES - 1) - 1))
{
// Small allocations are more likely. Improve
// branch prediction by placing this case first.
return capptr_reveal(small_alloc<zero_mem>(size));
// Perform the - 1 on size, so that zero wraps around and ends up on
// slow path.
if (SNMALLOC_LIKELY(
(size - 1) <= (sizeclass_to_size(NUM_SMALL_SIZECLASSES - 1) - 1)))
{
return capptr_reveal(small_alloc<zero_mem>(size));
}

return capptr_reveal(alloc_not_small<zero_mem>(size));
}
else
{
if (SNMALLOC_UNLIKELY(
(size - 1) <= (sizeclass_to_size(NUM_SMALL_SIZECLASSES - 1) - 1)))
{
return capptr_reveal(small_alloc_slow<zero_mem>(size));
}

return capptr_reveal(alloc_not_small<zero_mem>(size));
return capptr_reveal(alloc_not_small_fast<zero_mem>(size));
}
#endif
}

template<ZeroMem zero_mem = NoZero>
SNMALLOC_FAST_PATH ALLOCATOR void* alloc(size_t size)
{
// Small allocations are more likely
return alloc_hinted<1, zero_mem>(size);
}

/**
* Allocate memory of a statically known size.
*/
template<size_t size, ZeroMem zero_mem = NoZero>
SNMALLOC_FAST_PATH ALLOCATOR void* alloc()
{
return alloc<zero_mem>(size);
return alloc_hinted<size, zero_mem>(size);
}

/*
Expand Down