19de27fdaf
This adds some branch predictor and cache hints to the fast path of processing remote deallocation. It also removes the batching.
95 lines
2.8 KiB
C++
95 lines
2.8 KiB
C++
#pragma once
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#include "../ds/bits.h"
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#include "../pal/pal.h"
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namespace snmalloc
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{
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// 0 intermediate bits results in power of 2 small allocs. 1 intermediate
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// bit gives additional sizeclasses at the midpoint between each power of 2.
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// 2 intermediate bits gives 3 intermediate sizeclasses, etc.
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static constexpr size_t INTERMEDIATE_BITS =
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#ifdef USE_INTERMEDIATE_BITS
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USE_INTERMEDIATE_BITS
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#else
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2
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#endif
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;
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// Return remote small allocs when the local cache reaches this size.
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static constexpr int64_t REMOTE_CACHE =
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#ifdef USE_REMOTE_CACHE
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USE_REMOTE_CACHE
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#else
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1 << 20
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#endif
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;
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enum DecommitStrategy
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{
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/**
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* Never decommit memory.
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*/
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DecommitNone,
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/**
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* Decommit superslabs when they are entirely empty.
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*/
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DecommitSuper,
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/**
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* Decommit superslabs only when we are informed of memory pressure by the
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* OS, do not decommit anything in normal operation.
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*/
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DecommitSuperLazy
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};
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static constexpr DecommitStrategy decommit_strategy =
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#ifdef USE_DECOMMIT_STRATEGY
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USE_DECOMMIT_STRATEGY
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#elif defined(_WIN32) && !defined(OPEN_ENCLAVE)
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DecommitSuperLazy
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#else
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DecommitSuper
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#endif
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;
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// The remaining values are derived, not configurable.
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static constexpr size_t POINTER_BITS =
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bits::next_pow2_bits_const(sizeof(uintptr_t));
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// Used to isolate values on cache lines to prevent false sharing.
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static constexpr size_t CACHELINE_SIZE = 64;
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// Minimum allocation size is space for two pointers.
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static_assert(bits::next_pow2_const(sizeof(void*)) == sizeof(void*));
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static constexpr size_t MIN_ALLOC_SIZE = 2 * sizeof(void*);
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static constexpr size_t MIN_ALLOC_BITS = bits::ctz_const(MIN_ALLOC_SIZE);
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// Minimum slab size.
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static constexpr size_t MIN_CHUNK_BITS = bits::max(
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static_cast<size_t>(14), bits::next_pow2_bits_const(OS_PAGE_SIZE));
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static constexpr size_t MIN_CHUNK_SIZE = bits::one_at_bit(MIN_CHUNK_BITS);
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// Minimum number of objects on a slab
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#ifdef SNMALLOC_CHECK_CLIENT
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static constexpr size_t MIN_OBJECT_COUNT = 13;
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#else
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static constexpr size_t MIN_OBJECT_COUNT = 4;
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#endif
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// Maximum size of an object that uses sizeclasses.
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static constexpr size_t MAX_SIZECLASS_BITS = 16;
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static constexpr size_t MAX_SIZECLASS_SIZE =
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bits::one_at_bit(MAX_SIZECLASS_BITS);
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// Number of slots for remote deallocation.
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static constexpr size_t REMOTE_SLOT_BITS = 8;
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static constexpr size_t REMOTE_SLOTS = 1 << REMOTE_SLOT_BITS;
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static constexpr size_t REMOTE_MASK = REMOTE_SLOTS - 1;
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static_assert(
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INTERMEDIATE_BITS < MIN_ALLOC_BITS,
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"INTERMEDIATE_BITS must be less than MIN_ALLOC_BITS");
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static_assert(
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MIN_ALLOC_SIZE >= (sizeof(void*) * 2),
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"MIN_ALLOC_SIZE must be sufficient for two pointers");
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} // namespace snmalloc
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