add maxmemory_margin to allow for forcibly freeing more than the bare minimum,...

add maxmemory_margin to allow for forcibly freeing more than the bare minimum, and making space for new entries. track the count of expired and forcibly expired items.

src/config.c

@@ -123,6 +123,8 @@ void loadServerConfig(char *filename) {
             server.maxclients = atoi(argv[1]);
         } else if (!strcasecmp(argv[0],"maxmemory") && argc == 2) {
             server.maxmemory = memtoll(argv[1],NULL);
+        } else if (!strcasecmp(argv[0],"maxmemory_margin") && argc == 2) {
+            server.maxmemory_margin = memtoll(argv[1],NULL);
         } else if (!strcasecmp(argv[0],"memory_pressure_selection") && argc == 2) {
             server.memory_pressure_selection = atoi(argv[1]);
         } else if (!strcasecmp(argv[0],"slaveof") && argc == 3) {

src/redis.c

@@ -471,6 +471,7 @@ void activeExpireCycle(void) {
                     dbDelete(db,keyobj);
                     decrRefCount(keyobj);
                     expired++;
+                    db->expired_count++;
                     server.stat_expiredkeys++;
                 }
             }
@@ -734,6 +735,7 @@ void initServerConfig() {
     server.maxclients = 0;
     server.blpop_blocked_clients = 0;
     server.maxmemory = 0;
+    server.maxmemory_margin = 0;
     server.memory_pressure_selection = 3;
     server.vm_enabled = 0;
     server.vm_swap_file = zstrdup("/tmp/redis-%p.vm");
@@ -803,6 +805,8 @@ void initServer() {
         if (server.vm_enabled)
             server.db[j].io_keys = dictCreate(&keylistDictType,NULL);
         server.db[j].id = j;
+        server.db[j].expired_count = 0;
+        server.db[j].prematurely_expired_count = 0;
     }
     server.pubsub_channels = dictCreate(&keylistDictType,NULL);
     server.pubsub_patterns = listCreate();
@@ -1257,8 +1261,8 @@ sds genRedisInfoString(void) {
         keys = dictSize(server.db[j].dict);
         vkeys = dictSize(server.db[j].expires);
         if (keys || vkeys) {
-            info = sdscatprintf(info, "db%d:keys=%lld,expires=%lld\r\n",
-                j, keys, vkeys);
+            info = sdscatprintf(info, "db%d:keys=%lld,expires=%lld,expired=%lu,premature=%lu\r\n",
+                j, keys, vkeys, server.db[j].expired_count, server.db[j].prematurely_expired_count);
         }
     }
     return info;
@@ -1317,7 +1321,7 @@ int tryFreeOneObjectFromFreelist(void) {
  * memory usage.
  */
 void freeMemoryIfNeeded(void) {
-    while (server.maxmemory && zmalloc_used_memory() > server.maxmemory) {
+    while (server.maxmemory && zmalloc_used_memory() + server.maxmemory_margin > server.maxmemory) {
         int j, k, freed = 0;
 
         if (tryFreeOneObjectFromFreelist() == REDIS_OK) continue;
@@ -1343,6 +1347,8 @@ void freeMemoryIfNeeded(void) {
 
                 dictDelete(server.db[j].expires,minkey);
                 dictDelete(server.db[j].dict,minkey);
+                server.db[j].expired_count++;
+                server.db[j].prematurely_expired_count++;
             }
         }
         if (!freed) return; /* nothing to free... */

src/redis.h

@@ -260,6 +260,8 @@ typedef struct redisDb {
     dict *io_keys;              /* Keys with clients waiting for VM I/O */
     dict *watched_keys;         /* WATCHED keys for MULTI/EXEC CAS */
     int id;
+    unsigned long expired_count;
+    unsigned long prematurely_expired_count;
 } redisDb;
 
 /* Client MULTI/EXEC state */
@@ -381,6 +383,7 @@ struct redisServer {
     int replstate;
     unsigned int maxclients;
     unsigned long long maxmemory;
+    unsigned long long maxmemory_margin; /* bytes to keep free for new data */
     int memory_pressure_selection; /* # of candidates to choose from in freeMemoryIfNeeded(). */
     unsigned int blpop_blocked_clients;
     unsigned int vm_blocked_clients;