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Add configuration option for small address spaces

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This adds a configuration option for 1MiB superslabs with 16KiB slabs.
This commit is contained in:
Matthew Parkinson
2019-01-17 14:08:43 +00:00
parent b097b47aa2
commit 164df40372
1 changed files with 19 additions and 8 deletions
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27
src/mem/allocconfig.h
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@@ -39,6 +39,17 @@ namespace snmalloc
#endif
;
// Specifies smaller slab and super slab sizes for address space
// constrained scenarios.
static constexpr size_t ADDRESS_SPACE_CONSTRAINED =
#ifdef IS_ADDRESS_SPACE_CONSTRAINED
true
#else
// In 32 bit uses smaller superslab.
(!bits::is64())
#endif
;
static constexpr size_t RESERVE_MULTIPLE =
#ifdef USE_RESERVE_MULTIPLE
USE_RESERVE_MULTIPLE
@@ -70,10 +81,10 @@ namespace snmalloc
// Used to keep Superslab metadata committed.
static constexpr size_t OS_PAGE_SIZE = 0x1000;
static constexpr size_t PAGE_ALIGNED_SIZE = OS_PAGE_SIZE << INTERMEDIATE_BITS;
// Some system headers (e.g. Linux' sys/user.h, FreeBSD's machine/param.h)
// define `PAGE_SIZE` as a macro. We don't use `PAGE_SIZE` as our variable
// name, to avoid conflicts, but if we do see a macro definition then check
// that our value matches the platform's expected value.
// Some system headers (e.g. Linux' sys/user.h, FreeBSD's machine/param.h)
// define `PAGE_SIZE` as a macro. We don't use `PAGE_SIZE` as our variable
// name, to avoid conflicts, but if we do see a macro definition then check
// that our value matches the platform's expected value.
#ifdef PAGE_SIZE
static_assert(
PAGE_SIZE == OS_PAGE_SIZE,
@@ -85,14 +96,14 @@ namespace snmalloc
static constexpr size_t MIN_ALLOC_SIZE = 1 << MIN_ALLOC_BITS;
// Slabs are 64 kb.
static constexpr size_t SLAB_BITS = 16;
static constexpr size_t SLAB_BITS = ADDRESS_SPACE_CONSTRAINED ? 14 : 16;
static constexpr size_t SLAB_SIZE = 1 << SLAB_BITS;
static constexpr size_t SLAB_MASK = ~(SLAB_SIZE - 1);
// Superslabs are composed of this many slabs. Slab offsets are encoded as
// a byte, so the maximum count is 256. This must be a power of two to
// allow fast masking to find a superslab start address.
static constexpr size_t SLAB_COUNT_BITS = 8;
static constexpr size_t SLAB_COUNT_BITS = ADDRESS_SPACE_CONSTRAINED ? 6 : 8;
static constexpr size_t SLAB_COUNT = 1 << SLAB_COUNT_BITS;
static constexpr size_t SUPERSLAB_SIZE = SLAB_SIZE * SLAB_COUNT;
static constexpr size_t SUPERSLAB_MASK = ~(SUPERSLAB_SIZE - 1);
@@ -111,8 +122,8 @@ namespace snmalloc
MIN_ALLOC_SIZE >= (sizeof(void*) * 2),
"MIN_ALLOC_SIZE must be sufficient for two pointers");
static_assert(
SLAB_BITS == (sizeof(uint16_t) * 8),
"SLAB_BITS must be the bits in a uint16_t");
SLAB_BITS <= (sizeof(uint16_t) * 8),
"SLAB_BITS must not be more than the bits in a uint16_t");
static_assert(
SLAB_COUNT == bits::next_pow2_const(SLAB_COUNT),
"SLAB_COUNT must be a power of 2");