autofs-5.0.4 - make hash table scale to thousands of entries

From: Valerie Aurora Henson <vaurora@redhat.com>

Originally written by Paul Wankadia <junyer@google.com>.

The autofs cache lookup performs poorly for large maps.

The additive hashing algorithm used by autofs results in a clustering

of hash values around the average hash chain size. It is biased toward

a small range of hash indexes which becomes worse as the hash table size

increases.

Simple testing shows that the "One-at-a-time" hash function (implemented

by this patch) gives a much better distribution of hash indexes as table

size increases.

The only change made to the original patch is to make the hash table size

configurable with a default somewhat larger than it is currently.

---

 CHANGELOG                      |    2 ++

 include/automount.h            |    2 +-

 include/defaults.h             |    3 +++

 lib/cache.c                    |   47 +++++++++++++++++++++++-----------------

 lib/defaults.c                 |   16 +++++++++++++-

 redhat/autofs.sysconfig.in     |    6 +++++

 samples/autofs.conf.default.in |    6 +++++

 7 files changed, 60 insertions(+), 22 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG

index 0fb7db5..912c088 100644

--- a/CHANGELOG

+++ b/CHANGELOG

@@ -5,6 +5,8 @@

 - fix negative caching for non-existent map keys.

 - use CLOEXEC flag.

 - fix select(2) fd limit.

+- make hash table scale to thousands of entries (Paul Wankadia,

+  Valerie Aurora Henson).

 4/11/2008 autofs-5.0.4

 -----------------------

diff --git a/include/automount.h b/include/automount.h

index a55ddbc..fa24885 100644

--- a/include/automount.h

+++ b/include/automount.h

@@ -128,7 +128,7 @@ struct autofs_point;

 #define CHE_DUPLICATE	0x0020

 #define CHE_UNAVAIL	0x0040

-#define HASHSIZE		77

+#define NULL_MAP_HASHSIZE	64

 #define NEGATIVE_TIMEOUT	10

 #define UMOUNT_RETRIES		8

 #define EXPIRE_RETRIES		3

diff --git a/include/defaults.h b/include/defaults.h

index 12534ec..9a2430f 100644

--- a/include/defaults.h

+++ b/include/defaults.h

@@ -40,6 +40,8 @@

 #define DEFAULT_APPEND_OPTIONS		1

 #define DEFAULT_AUTH_CONF_FILE		AUTOFS_MAP_DIR "/autofs_ldap_auth.conf"

+#define DEFAULT_MAP_HASH_TABLE_SIZE	1024

+

 struct ldap_schema;

 struct ldap_searchdn;

@@ -62,6 +64,7 @@ void defaults_free_searchdns(struct ldap_searchdn *);

 unsigned int defaults_get_append_options(void);

 unsigned int defaults_get_umount_wait(void);

 const char *defaults_get_auth_conf_file(void);

+unsigned int defaults_get_map_hash_table_size(void);

 #endif

diff --git a/lib/cache.c b/lib/cache.c

index 4a00367..edb3192 100644

--- a/lib/cache.c

+++ b/lib/cache.c

@@ -190,7 +190,7 @@ struct mapent_cache *cache_init(struct autofs_point *ap, struct map_source *map)

 	if (!mc)

 		return NULL;

-	mc->size = HASHSIZE;

+	mc->size = defaults_get_map_hash_table_size();

 	mc->hash = malloc(mc->size * sizeof(struct entry *));

 	if (!mc->hash) {

@@ -241,7 +241,7 @@ struct mapent_cache *cache_init_null_cache(struct master *master)

 	if (!mc)

 		return NULL;

-	mc->size = HASHSIZE;

+	mc->size = NULL_MAP_HASHSIZE;

 	mc->hash = malloc(mc->size * sizeof(struct entry *));

 	if (!mc->hash) {

@@ -279,29 +279,36 @@ struct mapent_cache *cache_init_null_cache(struct master *master)

 	return mc;

 }

-static unsigned int hash(const char *key)

+static u_int32_t hash(const char *key, unsigned int size)

 {

-	unsigned long hashval;

+	u_int32_t hashval;

 	char *s = (char *) key;

-	for (hashval = 0; *s != '\0';)

-		hashval += *s++;

+	for (hashval = 0; *s != '\0';) {

+		hashval += (unsigned char) *s++;

+		hashval += (hashval << 10);

+		hashval ^= (hashval >> 6);

+	}

+

+	hashval += (hashval << 3);

+	hashval ^= (hashval >> 11);

+	hashval += (hashval << 15);

-	return hashval % HASHSIZE;

+	return hashval % size;

 }

-static unsigned int ino_hash(dev_t dev, ino_t ino)

+static u_int32_t ino_hash(dev_t dev, ino_t ino, unsigned int size)

 {

-	unsigned long hashval;

+	u_int32_t hashval;

 	hashval = dev + ino;

-	return hashval % HASHSIZE;

+	return hashval % size;

 }

 int cache_set_ino_index(struct mapent_cache *mc, const char *key, dev_t dev, ino_t ino)

 {

-	unsigned int ino_index = ino_hash(dev, ino);

+	u_int32_t ino_index = ino_hash(dev, ino, mc->size);

 	struct mapent *me;

 	me = cache_lookup_distinct(mc, key);

@@ -323,10 +330,10 @@ struct mapent *cache_lookup_ino(struct mapent_cache *mc, dev_t dev, ino_t ino)

 {

 	struct mapent *me = NULL;

 	struct list_head *head, *p;

-	unsigned int ino_index;

+	u_int32_t ino_index;

 	ino_index_lock(mc);

-	ino_index = ino_hash(dev, ino);

+	ino_index = ino_hash(dev, ino, mc->size);

 	head = &mc->ino_index[ino_index];

 	list_for_each(p, head) {

@@ -369,7 +376,7 @@ struct mapent *cache_lookup_first(struct mapent_cache *mc)

 struct mapent *cache_lookup_next(struct mapent_cache *mc, struct mapent *me)

 {

 	struct mapent *this;

-	unsigned long hashval;

+	u_int32_t hashval;

 	unsigned int i;

 	if (!me)

@@ -385,7 +392,7 @@ struct mapent *cache_lookup_next(struct mapent_cache *mc, struct mapent *me)

 		return this;

 	}

-	hashval = hash(me->key) + 1;

+	hashval = hash(me->key, mc->size) + 1;

 	if (hashval < mc->size) {

 		for (i = (unsigned int) hashval; i < mc->size; i++) {

 			this = mc->hash[i];

@@ -433,7 +440,7 @@ struct mapent *cache_lookup(struct mapent_cache *mc, const char *key)

 	if (!key)

 		return NULL;

-	for (me = mc->hash[hash(key)]; me != NULL; me = me->next) {

+	for (me = mc->hash[hash(key, mc->size)]; me != NULL; me = me->next) {

 		if (strcmp(key, me->key) == 0)

 			goto done;

 	}

@@ -446,7 +453,7 @@ struct mapent *cache_lookup(struct mapent_cache *mc, const char *key)

 			goto done;

 		}

-		for (me = mc->hash[hash("*")]; me != NULL; me = me->next)

+		for (me = mc->hash[hash("*", mc->size)]; me != NULL; me = me->next)

 			if (strcmp("*", me->key) == 0)

 				goto done;

 	}

@@ -462,7 +469,7 @@ struct mapent *cache_lookup_distinct(struct mapent_cache *mc, const char *key)

 	if (!key)

 		return NULL;

-	for (me = mc->hash[hash(key)]; me != NULL; me = me->next) {

+	for (me = mc->hash[hash(key, mc->size)]; me != NULL; me = me->next) {

 		if (strcmp(key, me->key) == 0)

 			return me;

 	}

@@ -530,7 +537,7 @@ int cache_add(struct mapent_cache *mc, struct map_source *ms, const char *key, c

 {

 	struct mapent *me, *existing = NULL;

 	char *pkey, *pent;

-	unsigned int hashval = hash(key);

+	u_int32_t hashval = hash(key, mc->size);

 	int status;

 	me = (struct mapent *) malloc(sizeof(struct mapent));

@@ -750,7 +757,7 @@ int cache_update(struct mapent_cache *mc, struct map_source *ms, const char *key

 int cache_delete(struct mapent_cache *mc, const char *key)

 {

 	struct mapent *me = NULL, *pred;

-	unsigned int hashval = hash(key);

+	u_int32_t hashval = hash(key, mc->size);

 	int status, ret = CHE_OK;

 	char *this;

diff --git a/lib/defaults.c b/lib/defaults.c

index ff653e3..0d39716 100644

--- a/lib/defaults.c

+++ b/lib/defaults.c

@@ -49,6 +49,8 @@

 #define ENV_UMOUNT_WAIT			"UMOUNT_WAIT"

 #define ENV_AUTH_CONF_FILE		"AUTH_CONF_FILE"

+#define ENV_MAP_HASH_TABLE_SIZE		"MAP_HASH_TABLE_SIZE"

+

 static const char *default_master_map_name = DEFAULT_MASTER_MAP_NAME;

 static const char *default_auth_conf_file  = DEFAULT_AUTH_CONF_FILE;

@@ -323,7 +325,8 @@ unsigned int defaults_read_config(unsigned int to_syslog)

 		    check_set_config_value(key, ENV_NAME_VALUE_ATTR, value, to_syslog) ||

 		    check_set_config_value(key, ENV_APPEND_OPTIONS, value, to_syslog) ||

 		    check_set_config_value(key, ENV_UMOUNT_WAIT, value, to_syslog) ||

-		    check_set_config_value(key, ENV_AUTH_CONF_FILE, value, to_syslog))

+		    check_set_config_value(key, ENV_AUTH_CONF_FILE, value, to_syslog) ||

+		    check_set_config_value(key, ENV_MAP_HASH_TABLE_SIZE, value, to_syslog))

 			;

 	}

@@ -672,3 +675,14 @@ const char *defaults_get_auth_conf_file(void)

 	return (const char *) cf;

 }

+unsigned int defaults_get_map_hash_table_size(void)

+{

+	long size;

+

+	size = get_env_number(ENV_MAP_HASH_TABLE_SIZE);

+	if (size < 0)

+		size = DEFAULT_MAP_HASH_TABLE_SIZE;

+

+	return (unsigned int) size;

+}

+

diff --git a/redhat/autofs.sysconfig.in b/redhat/autofs.sysconfig.in

index 8256888..fe36f45 100644

--- a/redhat/autofs.sysconfig.in

+++ b/redhat/autofs.sysconfig.in

@@ -89,6 +89,12 @@ BROWSE_MODE="no"

 #

 #AUTH_CONF_FILE="@@autofsmapdir@@/autofs_ldap_auth.conf"

 #

+# MAP_HASH_TABLE_SIZE - set the map cache hash table size.

+# 			Should be a power of 2 with a ratio roughly

+# 			between 1:10 and 1:20 for each map.

+#

+#MAP_HASH_TABLE_SIZE=1024

+#

 # General global options

 #

 # If the kernel supports using the autofs miscellanous device

diff --git a/samples/autofs.conf.default.in b/samples/autofs.conf.default.in

index 844a6f3..4496738 100644

--- a/samples/autofs.conf.default.in

+++ b/samples/autofs.conf.default.in

@@ -89,6 +89,12 @@ BROWSE_MODE="no"

 #

 #AUTH_CONF_FILE="@@autofsmapdir@@/autofs_ldap_auth.conf"

 #

+# MAP_HASH_TABLE_SIZE - set the map cache hash table size.

+# 			Should be a power of 2 with a ratio roughly

+# 			between 1:10 and 1:20 for each map.

+#

+#MAP_HASH_TABLE_SIZE=1024

+#

 # General global options

 #

 # If the kernel supports using the autofs miscellanous device