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Move link out of object space.

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The link object was previously stored in a disused object.  This is
good for reducing meta-data, but if we want to reduce the meta-data
corruption potential, then this is not a good design choice.

This commit moves it into the Metaslab.
This commit is contained in:
Matthew Parkinson
2021-03-12 21:11:43 +00:00
committed by Matthew Parkinson
parent e7dce55f19
commit 59edf294d0
5 changed files with 75 additions and 107 deletions
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72
src/mem/slab.h
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@@ -4,12 +4,6 @@
namespace snmalloc
{
struct FreeListHead
{
// Use a value with bottom bit set for empty list.
void* value = nullptr;
};
class Slab
{
private:
@@ -26,62 +20,6 @@ namespace snmalloc
return super->get_meta(this);
}
SlabLink* get_link()
{
return get_meta().get_link(this);
}
/**
* Takes a free list out of a slabs meta data.
* Returns the link as the allocation, and places the free list into the
* `fast_free_list` for further allocations.
*/
template<ZeroMem zero_mem, SNMALLOC_CONCEPT(ConceptPAL) PAL>
SNMALLOC_FAST_PATH void*
alloc(SlabList& sl, FreeListHead& fast_free_list, size_t rsize)
{
// Read the head from the metadata stored in the superslab.
Metaslab& meta = get_meta();
SNMALLOC_ASSERT(meta.link != 1);
SNMALLOC_ASSERT(rsize == sizeclass_to_size(meta.sizeclass));
SNMALLOC_ASSERT(
sl.get_next() == (SlabLink*)pointer_offset(this, meta.link));
SNMALLOC_ASSERT(!meta.is_full());
meta.debug_slab_invariant(this);
// Put everything in allocators small_class free list.
fast_free_list.value = meta.head;
meta.head = nullptr;
// Return the link as the node for this allocation.
void* link = pointer_offset(this, meta.link);
void* p = remove_cache_friendly_offset(link, meta.sizeclass);
// Treat stealing the free list as allocating it all.
meta.needed = meta.allocated;
meta.set_full();
sl.get_next()->remove();
SNMALLOC_ASSERT(meta.is_start_of_object(p));
meta.debug_slab_invariant(this);
if constexpr (zero_mem == YesZero)
{
if (rsize < PAGE_ALIGNED_SIZE)
PAL::zero(p, rsize);
else
PAL::template zero<true>(p, rsize);
}
else
{
UNUSED(rsize);
}
return p;
}
/**
* Given a bumpptr and a fast_free_list head reference, builds a new free
* list, and stores it in the fast_free_list. It will only create a page
@@ -158,21 +96,19 @@ namespace snmalloc
return super->dealloc_slab(this);
}
// Update the head and the sizeclass link.
uint16_t index = pointer_to_index(p);
SNMALLOC_ASSERT(meta.head == nullptr);
// SNMALLOC_ASSERT(meta.fully_allocated(is_short()));
meta.link = index;
meta.head = p;
Metaslab::store_next(p, nullptr);
meta.needed = meta.allocated - 1;
// Push on the list of slabs for this sizeclass.
sl->insert_prev(meta.get_link(this));
sl->insert_prev(&meta);
meta.debug_slab_invariant(this);
return Superslab::NoSlabReturn;
}
// Remove from the sizeclass list and dealloc on the superslab.
meta.get_link(this)->remove();
meta.remove();
if (is_short())
return super->dealloc_short_slab();