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Refactor use of sizeclasses (#415)

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The primary aim for this refactor is to use a representation for
sizeclasses that uniformly covers both large and small.  This allows
certain operations such as alloc_size and external_pointer to be
uniformly implemented.

The additional types make clear which kind of sizeclass is in use.

This also tidies up the code for sizeclass based divisible by and
modulus.

It fixes a bug in rust_realloc that didn't correctly determine a realloc
was required for large classes.
This commit is contained in:
Matthew Parkinson
2021-11-10 16:35:44 +00:00
committed by GitHub
parent 02f36a4b31
commit 3d403aef7f
19 changed files with 465 additions and 273 deletions
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28
src/mem/metaslab.h
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@@ -73,7 +73,7 @@ namespace snmalloc
/**
* Initialise Metaslab for a slab.
*/
void initialise(sizeclass_t sizeclass)
void initialise(smallsizeclass_t sizeclass)
{
free_queue.init();
// Set up meta data as if the entire slab has been turned into a free
@@ -112,7 +112,7 @@ namespace snmalloc
* and will return true, otherwise it will return false.
*/
SNMALLOC_FAST_PATH bool
set_sleeping(sizeclass_t sizeclass, uint16_t remaining)
set_sleeping(smallsizeclass_t sizeclass, uint16_t remaining)
{
auto threshold = threshold_for_waking_slab(sizeclass);
if (remaining >= threshold)
@@ -130,7 +130,7 @@ namespace snmalloc
return true;
}
SNMALLOC_FAST_PATH void set_not_sleeping(sizeclass_t sizeclass)
SNMALLOC_FAST_PATH void set_not_sleeping(smallsizeclass_t sizeclass)
{
auto allocated = sizeclass_to_slab_object_count(sizeclass);
needed() = allocated - threshold_for_waking_slab(sizeclass);
@@ -145,9 +145,9 @@ namespace snmalloc
}
static SNMALLOC_FAST_PATH bool
is_start_of_object(sizeclass_t sizeclass, address_t p)
is_start_of_object(smallsizeclass_t sizeclass, address_t p)
{
return is_multiple_of_sizeclass(
return divisible_by_sizeclass(
sizeclass,
p - (bits::align_down(p, sizeclass_to_slab_size(sizeclass))));
}
@@ -170,7 +170,7 @@ namespace snmalloc
Metaslab* meta,
freelist::Iter<>& fast_free_list,
LocalEntropy& entropy,
sizeclass_t sizeclass)
smallsizeclass_t sizeclass)
{
auto& key = entropy.get_free_list_key();
@@ -213,8 +213,8 @@ namespace snmalloc
*
* * log_2(size), at least MIN_CHUNK_BITS, for large allocations.
*
* * a value in [0, NUM_SIZECLASSES] for small allocations. These may be
* directly passed to the sizeclass (not slab_sizeclass) functions of
* * a value in [0, NUM_SMALL_SIZECLASSES] for small allocations. These
* may be directly passed to the sizeclass (not slab_sizeclass) functions of
* sizeclasstable.h
*
*/
@@ -235,12 +235,15 @@ namespace snmalloc
{}
SNMALLOC_FAST_PATH
MetaEntry(Metaslab* meta, RemoteAllocator* remote, sizeclass_t sizeclass)
MetaEntry(
Metaslab* meta,
RemoteAllocator* remote,
sizeclass_t sizeclass = sizeclass_t())
: meta(meta)
{
/* remote might be nullptr; cast to uintptr_t before offsetting */
remote_and_sizeclass =
pointer_offset(reinterpret_cast<uintptr_t>(remote), sizeclass);
pointer_offset(reinterpret_cast<uintptr_t>(remote), sizeclass.raw());
}
/**
@@ -285,8 +288,9 @@ namespace snmalloc
{
// TODO: perhaps remove static_cast with resolution of
// https://github.com/CTSRD-CHERI/llvm-project/issues/588
return static_cast<sizeclass_t>(remote_and_sizeclass) &
(alignof(RemoteAllocator) - 1);
return sizeclass_t::from_raw(
static_cast<size_t>(remote_and_sizeclass) &
(alignof(RemoteAllocator) - 1));
}
};