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Avoid atomic operations for dependent rtree reads.

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This commit is contained in:
Jason Evans 2015-05-15 17:02:30 -07:00
parent c451831264
commit fd5f9e43c3
5 changed files with 43 additions and 26 deletions
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31
include/jemalloc/internal/rtree.h
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@ -114,13 +114,14 @@ bool rtree_node_valid(rtree_node_elm_t *node);
rtree_node_elm_t *rtree_child_tryread(rtree_node_elm_t *elm);
rtree_node_elm_t *rtree_child_read(rtree_t *rtree, rtree_node_elm_t *elm,
unsigned level);
extent_node_t *rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm);
extent_node_t *rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm,
bool dependent);
void rtree_val_write(rtree_t *rtree, rtree_node_elm_t *elm,
const extent_node_t *val);
rtree_node_elm_t *rtree_subtree_tryread(rtree_t *rtree, unsigned level);
rtree_node_elm_t *rtree_subtree_read(rtree_t *rtree, unsigned level);
extent_node_t *rtree_get(rtree_t *rtree, uintptr_t key);
extent_node_t *rtree_get(rtree_t *rtree, uintptr_t key, bool dependent);
bool rtree_set(rtree_t *rtree, uintptr_t key, const extent_node_t *val);
#endif
@ -179,10 +180,25 @@ rtree_child_read(rtree_t *rtree, rtree_node_elm_t *elm, unsigned level)
}
JEMALLOC_INLINE extent_node_t *
rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm)
rtree_val_read(rtree_t *rtree, rtree_node_elm_t *elm, bool dependent)
{
return (atomic_read_p(&elm->pun));
if (dependent) {
/*
* Reading a val on behalf of a pointer to a valid allocation is
* guaranteed to be a clean read even without synchronization,
* because the rtree update became visible in memory before the
* pointer came into existence.
*/
return (elm->val);
} else {
/*
* An arbitrary read, e.g. on behalf of ivsalloc(), may not be
* dependent on a previous rtree write, which means a stale read
* could result if synchronization were omitted here.
*/
return (atomic_read_p(&elm->pun));
}
}
JEMALLOC_INLINE void
@ -216,7 +232,7 @@ rtree_subtree_read(rtree_t *rtree, unsigned level)
}
JEMALLOC_INLINE extent_node_t *
rtree_get(rtree_t *rtree, uintptr_t key)
rtree_get(rtree_t *rtree, uintptr_t key, bool dependent)
{
uintptr_t subkey;
unsigned i, start_level;
@ -226,7 +242,7 @@ rtree_get(rtree_t *rtree, uintptr_t key)
for (i = start_level, node = rtree_subtree_tryread(rtree, start_level);
/**/; i++, node = child) {
if (unlikely(!rtree_node_valid(node)))
if (!dependent && unlikely(!rtree_node_valid(node)))
return (NULL);
subkey = rtree_subkey(rtree, key, i);
if (i == rtree->height - 1) {
@ -234,7 +250,8 @@ rtree_get(rtree_t *rtree, uintptr_t key)
* node is a leaf, so it contains values rather than
* child pointers.
*/
return (rtree_val_read(rtree, &node[subkey]));
return (rtree_val_read(rtree, &node[subkey],
dependent));
}
assert(i < rtree->height - 1);
child = rtree_child_tryread(&node[subkey]);