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authorJeff Darcy <jdarcy@redhat.com>2012-03-29 12:47:49 -0400
committerAnand Avati <avati@redhat.com>2012-06-01 12:15:07 -0700
commite8eb0a9cb6539a7607d4c134daf331400a93d136 (patch)
tree6642d790b6cb130aaa70b30359b361eaffc78cbc /libglusterfs
parent27620d0f7d9b101cc47a13a23928f767248a8cff (diff)
Optimize for small dicts, and avoid an overrun.
As dicts get used more and more in the I/O path (especially for xattrs and the new xdata feature), removing some of their inherent inefficiency becomes more important. This patch addresses some of the issues around allocating data_pair_t structures separately. Along the way, I found that the way we're allocating the "members" hash table was subtly wrong, and could lead to a memory overrun. This is a latent bug because nobody uses dict_get_new_full that way, but I added an assert to guard against that possibility. One beneficial side effect is that we now save four pointers' worth of space per dict, offsetting the extra space used for the new members. Change-Id: Ie8c3e49f1e584daec4b0d2d8ce9dafbc76fb57b2 BUG: 827448 Signed-off-by: Jeff Darcy <jdarcy@redhat.com> Reviewed-on: http://review.gluster.com/3040 Tested-by: Gluster Build System <jenkins@build.gluster.com> Reviewed-by: Anand Avati <avati@redhat.com>
Diffstat (limited to 'libglusterfs')
-rw-r--r--libglusterfs/src/dict.c96
-rw-r--r--libglusterfs/src/dict.h5
2 files changed, 68 insertions, 33 deletions
diff --git a/libglusterfs/src/dict.c b/libglusterfs/src/dict.c
index 9b0d7ff18b7..8048414705b 100644
--- a/libglusterfs/src/dict.c
+++ b/libglusterfs/src/dict.c
@@ -29,16 +29,6 @@
#include "byte-order.h"
#include "globals.h"
-data_pair_t *
-get_new_data_pair ()
-{
- data_pair_t *data_pair_ptr = NULL;
-
- data_pair_ptr = mem_get0 (THIS->ctx->dict_pair_pool);
-
- return data_pair_ptr;
-}
-
data_t *
get_new_data ()
{
@@ -63,11 +53,32 @@ get_new_dict_full (int size_hint)
}
dict->hash_size = size_hint;
- dict->members = mem_get0 (THIS->ctx->dict_pair_pool);
-
- if (!dict->members) {
- mem_put (dict);
- return NULL;
+ if (size_hint == 1) {
+ /*
+ * This is the only case we ever see currently. If we ever
+ * need to support resizing the hash table, the resize function
+ * will have to take into account the possibility that
+ * "members" is not separately allocated (i.e. don't just call
+ * realloc() blindly.
+ */
+ dict->members = &dict->members_internal;
+ }
+ else {
+ /*
+ * We actually need to allocate space for size_hint *pointers*
+ * but we actually allocate space for one *structure*. Since
+ * a data_pair_t consists of five pointers, we're wasting four
+ * pointers' worth for N=1, and will overrun what we allocated
+ * for N>5. If anybody ever starts using size_hint, we'll need
+ * to fix this.
+ */
+ GF_ASSERT (size_hint <=
+ (sizeof(data_pair_t) / sizeof(data_pair_t *)));
+ dict->members = mem_get0 (THIS->ctx->dict_pair_pool);
+ if (!dict->members) {
+ mem_put (dict);
+ return NULL;
+ }
}
LOCK_INIT (&dict->lock);
@@ -251,22 +262,36 @@ _dict_set (dict_t *this,
/* Indicates duplicate key */
return 0;
}
- pair = mem_get0 (THIS->ctx->dict_pair_pool);
- if (!pair) {
- return -1;
+ if (this->free_pair_in_use) {
+ pair = mem_get0 (THIS->ctx->dict_pair_pool);
+ if (!pair) {
+ return -1;
+ }
}
-
- pair->key = (char *) GF_CALLOC (1, strlen (key) + 1,
- gf_common_mt_char);
- if (!pair->key) {
- mem_put (pair);
-
- if (key_free)
- GF_FREE (key);
- return -1;
+ else {
+ pair = &this->free_pair;
+ this->free_pair_in_use = _gf_true;
}
- strcpy (pair->key, key);
+ if (key_free) {
+ /* It's ours. Use it. */
+ pair->key = key;
+ key_free = 0;
+ }
+ else {
+ pair->key = (char *) GF_CALLOC (1, strlen (key) + 1,
+ gf_common_mt_char);
+ if (!pair->key) {
+ if (pair == &this->free_pair) {
+ this->free_pair_in_use = _gf_false;
+ }
+ else {
+ mem_put (pair);
+ }
+ return -1;
+ }
+ strcpy (pair->key, key);
+ }
pair->value = data_ref (value);
pair->hash_next = this->members[hashval];
@@ -363,7 +388,12 @@ dict_del (dict_t *this, char *key)
pair->next->prev = pair->prev;
GF_FREE (pair->key);
- mem_put (pair);
+ if (pair == &this->free_pair) {
+ this->free_pair_in_use = _gf_false;
+ }
+ else {
+ mem_put (pair);
+ }
this->count--;
break;
}
@@ -394,11 +424,15 @@ dict_destroy (dict_t *this)
pair = pair->next;
data_unref (prev->value);
GF_FREE (prev->key);
- mem_put (prev);
+ if (prev != &this->free_pair) {
+ mem_put (prev);
+ }
prev = pair;
}
- mem_put (this->members);
+ if (this->members != &this->members_internal) {
+ mem_put (this->members);
+ }
if (this->extra_free)
GF_FREE (this->extra_free);
diff --git a/libglusterfs/src/dict.h b/libglusterfs/src/dict.h
index 4e7cf2406eb..2a875039661 100644
--- a/libglusterfs/src/dict.h
+++ b/libglusterfs/src/dict.h
@@ -99,6 +99,9 @@ struct _dict {
char *extra_free;
char *extra_stdfree;
gf_lock_t lock;
+ data_pair_t *members_internal;
+ data_pair_t free_pair;
+ gf_boolean_t free_pair_in_use;
};
@@ -165,8 +168,6 @@ data_t * data_copy (data_t *old);
dict_t *get_new_dict_full (int size_hint);
dict_t *get_new_dict ();
-data_pair_t *get_new_data_pair ();
-
void dict_foreach (dict_t *this,
void (*fn)(dict_t *this,
char *key,