add memory_pressure_selection config.

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],"memory_pressure_selection") && argc == 2) {
+            server.memory_pressure_selection = atoi(argv[1]);
         } else if (!strcasecmp(argv[0],"slaveof") && argc == 3) {
             server.masterhost = sdsnew(argv[1]);
             server.masterport = atoi(argv[2]);

src/redis.c

@@ -733,6 +733,7 @@ void initServerConfig() {
     server.maxclients = 0;
     server.blpop_blocked_clients = 0;
     server.maxmemory = 0;
+    server.memory_pressure_selection = 3;
     server.vm_enabled = 0;
     server.vm_swap_file = zstrdup("/tmp/redis-%p.vm");
     server.vm_page_size = 256;          /* 256 bytes per page */
@@ -1328,7 +1329,7 @@ void freeMemoryIfNeeded(void) {
                 freed = 1;
                 /* From a sample of three keys drop the one nearest to
                  * the natural expire */
-                for (k = 0; k < 3; k++) {
+                for (k = 0; k < server.memory_pressure_selection; k++) {
                     time_t t;
 
                     de = dictGetRandomKey(server.db[j].expires);

src/redis.h

@@ -381,6 +381,7 @@ struct redisServer {
     int replstate;
     unsigned int maxclients;
     unsigned long long maxmemory;
+    int memory_pressure_selection; /* # of candidates to choose from in freeMemoryIfNeeded(). */
     unsigned int blpop_blocked_clients;
     unsigned int vm_blocked_clients;
     /* Sort parameters - qsort_r() is only available under BSD so we