Fix apc_cache_default_expunge() to always remove expired entries

When apc_cache_default_expunge() is called, it now always cleans up
expired entries and doesn't skip cleanup anymore, as it is only called
when there is not enough memory available to store a cache entry and
cleanup is really needed. The skip can happen because the function
apc_sma_get_avail_mem() doesn't take into account that a block of
contiguous memory is needed. In situations with huge fragmentation,
the old behavior can cause apcu to not accept new entries anymore which
don't fit into a fragment of available memory. This causes php-functions
like apcu_store() to not being able to insert bigger entries, until the
cache has filled up enough with small entries to trigger the cleanup.
This commit fixes the issue and mostly implements a behavior that should
have already been implemented previously according to the header file.
This also applies to the smart configuration setting that is now used to
tune the probability of a full cache wipe.

Author: madmajestro

apc_cache.c

@@ -735,8 +735,7 @@ PHP_APCU_API void apc_cache_clear(apc_cache_t* cache)
 PHP_APCU_API void apc_cache_default_expunge(apc_cache_t* cache, size_t size)
 {
 	time_t t;
-	size_t suitable = 0L;
-	size_t available = 0L;
+	size_t i;
 
 	if (!cache) {
 		return;
@@ -751,43 +750,35 @@ PHP_APCU_API void apc_cache_default_expunge(apc_cache_t* cache, size_t size)
 		return;
 	}
 
-	/* make suitable selection */
-	suitable = (cache->smart > 0L) ? (size_t) (cache->smart * size) : (size_t) (cache->sma->size/2);
+	/* smart adjusts the required memory-size, to increase the probability of a full cache wipe */
+	size = (cache->smart > 0L) ? (size_t) (cache->smart * size) : size;
 
 	/* gc */
 	apc_cache_wlocked_gc(cache);
 
-	/* get available */
-	available = apc_sma_get_avail_mem(cache->sma);
-
-	/* check that expunge is necessary */
-	if (available < suitable) {
-		size_t i;
-
-		/* look for junk */
-		for (i = 0; i < cache->nslots; i++) {
-			apc_cache_entry_t **entry = &cache->slots[i];
-			while (*entry) {
-				if (apc_cache_entry_expired(cache, *entry, t)) {
-					apc_cache_wlocked_remove_entry(cache, entry);
-					continue;
-				}
-
-				/* grab next entry */
-				entry = &(*entry)->next;
+	/* remove expired entries */
+	for (i = 0; i < cache->nslots; i++) {
+		apc_cache_entry_t **entry = &cache->slots[i];
+		while (*entry) {
+			if (apc_cache_entry_expired(cache, *entry, t)) {
+				apc_cache_wlocked_remove_entry(cache, entry);
+				continue;
 			}
-		}
 
-		/* if the cache now has space, then reset last key */
-		if (apc_sma_get_avail_size(cache->sma, size)) {
-			/* wipe lastkey */
-			memset(&cache->header->lastkey, 0, sizeof(apc_cache_slam_key_t));
-		} else {
-			/* with not enough space left in cache, we are forced to expunge */
-			apc_cache_wlocked_real_expunge(cache);
+			/* grab next entry */
+			entry = &(*entry)->next;
 		}
 	}
 
+	/* if the cache now has space, then reset last key */
+	if (apc_sma_get_avail_size(cache->sma, size)) {
+		/* wipe lastkey */
+		memset(&cache->header->lastkey, 0, sizeof(apc_cache_slam_key_t));
+	} else {
+		/* with not enough space left in cache, we are forced to expunge */
+		apc_cache_wlocked_real_expunge(cache);
+	}
+
 	apc_cache_wunlock(cache);
 }
 /* }}} */

apc_cache.h

@@ -251,20 +251,12 @@ PHP_APCU_API void apc_cache_serializer(apc_cache_t* cache, const char* name);
 
 /* {{{ apc_cache_default_expunge
 * Where smart is not set:
-*  Where no ttl is set on cache:
-*   1) Perform cleanup of stale entries
-*   2) Expunge if available memory is less than sma->size/2
-*  Where ttl is set on cache:
-*   1) Perform cleanup of stale entries
-*   2) If available memory if less than the size requested, run full expunge
+*  1) Perform cleanup of stale entries
+*  2) If available memory is less than the size requested, run full expunge
 *
 * Where smart is set:
-*  Where no ttl is set on cache:
-*   1) Perform cleanup of stale entries
-*   2) Expunge is available memory is less than size * smart
-*  Where ttl is set on cache:
-*   1) Perform cleanup of stale entries
-*   2) If available memory if less than the size requested, run full expunge
+*  1) Perform cleanup of stale entries
+*  2) If available memory is less than the size requested * smart, run full expunge
 *
 * The TTL of an entry takes precedence over the TTL of a cache
 */