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Changes the representation in Metaslab Used

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Used is now set to 1, when the slab is full.  This means that the test
for
 used - 1 == 0
can be used to detect leaving full, and entering empty, reducing fast
path deallocation branchs by 1.
This commit is contained in:
Matthew Parkinson
2019-11-19 16:25:27 +00:00
parent b889f11d04
commit cb4b8fa545
3 changed files with 33 additions and 40 deletions
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32
src/mem/slab.h
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@@ -163,14 +163,9 @@ namespace snmalloc
error("Detected potential double free.");
#endif
meta.debug_slab_invariant(is_short(), this);
meta.sub_use();
bool was_full = meta.is_full();
if (unlikely(was_full))
return false;
bool is_unused = meta.is_unused();
if (unlikely(is_unused))
if (unlikely(meta.sub_use()))
return false;
// Update the head and the next pointer in the free list.
@@ -198,13 +193,10 @@ namespace snmalloc
{
Metaslab& meta = super->get_meta(this);
bool was_full = meta.is_full();
bool is_unused = meta.is_unused();
if (was_full)
if (meta.is_full())
{
// We are not on the sizeclass list.
if (is_unused)
if (meta.allocated == 1)
{
// Dealloc on the superslab.
if (is_short())
@@ -217,6 +209,7 @@ namespace snmalloc
assert(meta.head == 1);
// assert(meta.fully_allocated(is_short()));
meta.link = index;
meta.used = meta.allocated - 1;
// Push on the list of slabs for this sizeclass.
sl->insert_back(meta.get_link(this));
@@ -224,18 +217,13 @@ namespace snmalloc
return Superslab::NoSlabReturn;
}
if (is_unused)
{
// Remove from the sizeclass list and dealloc on the superslab.
sl->remove(meta.get_link(this));
// Remove from the sizeclass list and dealloc on the superslab.
sl->remove(meta.get_link(this));
if (is_short())
return super->dealloc_short_slab(memory_provider);
if (is_short())
return super->dealloc_short_slab(memory_provider);
return super->dealloc_slab(this, memory_provider);
}
abort();
return super->dealloc_slab(this, memory_provider);
}
bool is_short()