[ltt-dev] [PATCH 03/11] Move replace code out from _cds_lfht_add()
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Thu Oct 27 00:31:41 EDT 2011
I merged a significantly re-worked version of this patch. Thanks for
pointing out that the replacement could re-use the uniquify code path!
Mathieu
commit 83beee94416bdffdec505bc33cfd79859f6aa243
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date: Thu Oct 27 06:30:49 2011 +0200
Move replace code out from _cds_lfht_add()
Original patch from Lai Jiangshan, reworked significantly to keep the
iterator semantic, where a "next" node is never re-read after being
looked up within a RCU read-side critical section after it has been
validated.
Although strictly speaking the "replace" code re-checks that the next
node is not logically removed with a cmpxchg, I prefer to ensure that
all lookup paths behave similarly. It will make it easier to track
behavior later on if they all follow the same rules.
Reported-by: Lai Jiangshan <laijs at cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
diff --git a/rculfhash.c b/rculfhash.c
index be995df..b9c184f 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -262,17 +262,12 @@ struct partition_resize_work {
unsigned long start, unsigned long len);
};
-enum add_mode {
- ADD_DEFAULT = 0,
- ADD_UNIQUE = 1,
- ADD_REPLACE = 2,
-};
-
static
-struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
- unsigned long size,
- struct cds_lfht_node *node,
- enum add_mode mode, int dummy);
+void _cds_lfht_add(struct cds_lfht *ht,
+ unsigned long size,
+ struct cds_lfht_node *node,
+ struct cds_lfht_iter *unique_ret,
+ int dummy);
/*
* Algorithm to reverse bits in a word by lookup table, extended to
@@ -855,11 +850,16 @@ end:
}
}
+/*
+ * A non-NULL unique_ret pointer uses the "add unique" (or uniquify) add
+ * mode. A NULL unique_ret allows creation of duplicate keys.
+ */
static
-struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
- unsigned long size,
- struct cds_lfht_node *node,
- enum add_mode mode, int dummy)
+void _cds_lfht_add(struct cds_lfht *ht,
+ unsigned long size,
+ struct cds_lfht_node *node,
+ struct cds_lfht_iter *unique_ret,
+ int dummy)
{
struct cds_lfht_node *iter_prev, *iter, *next, *new_node, *new_next,
*return_node;
@@ -869,8 +869,9 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
assert(!is_removed(node));
if (!size) {
assert(dummy);
+ assert(!unique_ret);
node->p.next = flag_dummy(get_end());
- return node; /* Initial first add (head) */
+ return; /* Initial first add (head) */
}
lookup = lookup_bucket(ht, size, bit_reverse_ulong(node->p.reverse_hash));
for (;;) {
@@ -895,16 +896,15 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
next = rcu_dereference(clear_flag(iter)->p.next);
if (unlikely(is_removed(next)))
goto gc_node;
- if ((mode == ADD_UNIQUE || mode == ADD_REPLACE)
+ if (unique_ret
&& !is_dummy(next)
&& clear_flag(iter)->p.reverse_hash == node->p.reverse_hash
&& !ht->compare_fct(node->key, node->key_len,
clear_flag(iter)->key,
clear_flag(iter)->key_len)) {
- if (mode == ADD_UNIQUE)
- return clear_flag(iter);
- else /* mode == ADD_REPLACE */
- goto replace;
+ unique_ret->node = clear_flag(iter);
+ unique_ret->next = next;
+ return;
}
/* Only account for identical reverse hash once */
if (iter_prev->p.reverse_hash != clear_flag(iter)->p.reverse_hash
@@ -931,23 +931,10 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
new_node) != iter) {
continue; /* retry */
} else {
- if (mode == ADD_REPLACE)
- return_node = NULL;
- else /* ADD_DEFAULT and ADD_UNIQUE */
- return_node = node;
+ return_node = node;
goto end;
}
- replace:
-
- if (!_cds_lfht_replace(ht, size, clear_flag(iter), next,
- node)) {
- return_node = clear_flag(iter);
- goto end; /* gc already done */
- } else {
- continue; /* retry */
- }
-
gc_node:
assert(!is_removed(iter));
if (is_dummy(iter))
@@ -958,7 +945,10 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
/* retry */
}
end:
- return return_node;
+ if (unique_ret) {
+ unique_ret->node = return_node;
+ /* unique_ret->next left unset, never used. */
+ }
}
static
@@ -1094,8 +1084,8 @@ void init_table_populate_partition(struct cds_lfht *ht, unsigned long i,
i, j, !i ? 0 : (1UL << (i - 1)) + j);
new_node->p.reverse_hash =
bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
- (void) _cds_lfht_add(ht, !i ? 0 : (1UL << (i - 1)),
- new_node, ADD_DEFAULT, 1);
+ _cds_lfht_add(ht, !i ? 0 : (1UL << (i - 1)),
+ new_node, NULL, 1);
}
ht->cds_lfht_rcu_read_unlock();
}
@@ -1437,7 +1427,7 @@ void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node)
node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
size = rcu_dereference(ht->t.size);
- (void) _cds_lfht_add(ht, size, node, ADD_DEFAULT, 0);
+ _cds_lfht_add(ht, size, node, NULL, 0);
ht_count_add(ht, size);
}
@@ -1445,32 +1435,38 @@ struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
struct cds_lfht_node *node)
{
unsigned long hash, size;
- struct cds_lfht_node *ret;
+ struct cds_lfht_iter iter;
hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
size = rcu_dereference(ht->t.size);
- ret = _cds_lfht_add(ht, size, node, ADD_UNIQUE, 0);
- if (ret == node)
+ _cds_lfht_add(ht, size, node, &iter, 0);
+ if (iter.node == node)
ht_count_add(ht, size);
- return ret;
+ return iter.node;
}
struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
struct cds_lfht_node *node)
{
unsigned long hash, size;
- struct cds_lfht_node *ret;
+ struct cds_lfht_iter iter;
hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
size = rcu_dereference(ht->t.size);
- ret = _cds_lfht_add(ht, size, node, ADD_REPLACE, 0);
- if (ret == NULL)
- ht_count_add(ht, size);
- return ret;
+ for (;;) {
+ _cds_lfht_add(ht, size, node, &iter, 0);
+ if (iter.node == node) {
+ ht_count_add(ht, size);
+ return NULL;
+ }
+
+ if (!_cds_lfht_replace(ht, size, iter.node, iter.next, node))
+ return iter.node;
+ }
}
int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter,
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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