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Make dss operations lockless.

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Rather than protecting dss operations with a mutex, use atomic
operations.  This has negligible impact on synchronization overhead
during typical dss allocation, but is a substantial improvement for
chunk_in_dss() and the newly added chunk_dss_mergeable(), which can be
called multiple times during chunk deallocations.

This change also has the advantage of avoiding tsd in deallocation paths
associated with purging, which resolves potential deadlocks during
thread exit due to attempted tsd resurrection.

This resolves #425.
This commit is contained in:
Jason Evans
2016-10-13 12:18:38 -07:00
parent 9737685943
commit e2bcf037d4
11 changed files with 134 additions and 153 deletions
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src/chunk.c
+9 -37
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@@ -611,10 +611,10 @@ chunk_dalloc_cache(tsdn_t *tsdn, arena_t *arena, chunk_hooks_t *chunk_hooks,
}
static bool
chunk_dalloc_default_impl(tsdn_t *tsdn, void *chunk, size_t size)
chunk_dalloc_default_impl(void *chunk, size_t size)
{
if (!have_dss || !chunk_in_dss(tsdn, chunk))
if (!have_dss || !chunk_in_dss(chunk))
return (chunk_dalloc_mmap(chunk, size));
return (true);
}
@@ -623,11 +623,8 @@ static bool
chunk_dalloc_default(void *chunk, size_t size, bool committed,
unsigned arena_ind)
{
tsdn_t *tsdn;
tsdn = tsdn_fetch();
return (chunk_dalloc_default_impl(tsdn, chunk, size));
return (chunk_dalloc_default_impl(chunk, size));
}
void
@@ -645,7 +642,7 @@ chunk_dalloc_wrapper(tsdn_t *tsdn, arena_t *arena, chunk_hooks_t *chunk_hooks,
/* Try to deallocate. */
if (chunk_hooks->dalloc == chunk_dalloc_default) {
/* Call directly to propagate tsdn. */
err = chunk_dalloc_default_impl(tsdn, chunk, size);
err = chunk_dalloc_default_impl(chunk, size);
} else
err = chunk_hooks->dalloc(chunk, size, committed, arena->ind);
@@ -718,13 +715,12 @@ chunk_split_default(void *chunk, size_t size, size_t size_a, size_t size_b,
}
static bool
chunk_merge_default_impl(tsdn_t *tsdn, void *chunk_a, void *chunk_b)
chunk_merge_default_impl(void *chunk_a, void *chunk_b)
{
if (!maps_coalesce)
return (true);
if (have_dss && chunk_in_dss(tsdn, chunk_a) != chunk_in_dss(tsdn,
chunk_b))
if (have_dss && !chunk_dss_mergeable(chunk_a, chunk_b))
return (true);
return (false);
@@ -734,11 +730,8 @@ static bool
chunk_merge_default(void *chunk_a, size_t size_a, void *chunk_b, size_t size_b,
bool committed, unsigned arena_ind)
{
tsdn_t *tsdn;
tsdn = tsdn_fetch();
return (chunk_merge_default_impl(tsdn, chunk_a, chunk_b));
return (chunk_merge_default_impl(chunk_a, chunk_b));
}
static rtree_node_elm_t *
@@ -782,32 +775,11 @@ chunk_boot(void)
chunksize_mask = chunksize - 1;
chunk_npages = (chunksize >> LG_PAGE);
if (have_dss && chunk_dss_boot())
return (true);
if (have_dss)
chunk_dss_boot();
if (rtree_new(&chunks_rtree, (unsigned)((ZU(1) << (LG_SIZEOF_PTR+3)) -
opt_lg_chunk), chunks_rtree_node_alloc, NULL))
return (true);
return (false);
}
void
chunk_prefork(tsdn_t *tsdn)
{
chunk_dss_prefork(tsdn);
}
void
chunk_postfork_parent(tsdn_t *tsdn)
{
chunk_dss_postfork_parent(tsdn);
}
void
chunk_postfork_child(tsdn_t *tsdn)
{
chunk_dss_postfork_child(tsdn);
}