make HOT/WARM ratios starttime tunable.

runtime tunable is difficult and may require either atomics, or adding an
extra items.c array. Adjusting the value would roll through and lock each
LRU before changing the value.

items.c

@@ -803,9 +803,9 @@ static int lru_pull_tail(const int orig_id, const int cur_lru,
         /* FIXME: Hardcoded percentage */
         switch (cur_lru) {
             case HOT_LRU:
-                limit = total_chunks * 32 / 100;
+                limit = total_chunks * settings.hot_lru_pct / 100;
             case WARM_LRU:
-                limit = total_chunks * 32 / 100;
+                limit = total_chunks * settings.warm_lru_pct / 100;
                 if (sizes[id] > limit) {
                     itemstats[id].moves_to_cold++;
                     move_to_lru = COLD_LRU;

memcached.c

@@ -236,6 +236,8 @@ static void settings_init(void) {
     settings.lru_crawler_sleep = 100;
     settings.lru_crawler_tocrawl = 0;
     settings.lru_maintainer_thread = false;
+    settings.hot_lru_pct = 32;
+    settings.warm_lru_pct = 32;
     settings.hashpower_init = 0;
     settings.slab_reassign = false;
     settings.slab_automove = 0;
@@ -2675,6 +2677,9 @@ static void process_stat_settings(ADD_STAT add_stats, void *c) {
     APPEND_STAT("tail_repair_time", "%d", settings.tail_repair_time);
     APPEND_STAT("flush_enabled", "%s", settings.flush_enabled ? "yes" : "no");
     APPEND_STAT("hash_algorithm", "%s", settings.hash_algorithm);
+    APPEND_STAT("lru_maintainer_thread", "%s", settings.lru_maintainer_thread ? "yes" : "no");
+    APPEND_STAT("hot_lru_pct", "%d", settings.hot_lru_pct);
+    APPEND_STAT("warm_lru_pct", "%d", settings.hot_lru_pct);
 }
 
 static void conn_to_str(const conn *c, char *buf) {
@@ -5077,7 +5082,9 @@ int main (int argc, char **argv) {
         LRU_CRAWLER,
         LRU_CRAWLER_SLEEP,
         LRU_CRAWLER_TOCRAWL,
-        LRU_MAINTAINER
+        LRU_MAINTAINER,
+        HOT_LRU_PCT,
+        WARM_LRU_PCT
     };
     char *const subopts_tokens[] = {
         [MAXCONNS_FAST] = "maxconns_fast",
@@ -5090,6 +5097,8 @@ int main (int argc, char **argv) {
         [LRU_CRAWLER_SLEEP] = "lru_crawler_sleep",
         [LRU_CRAWLER_TOCRAWL] = "lru_crawler_tocrawl",
         [LRU_MAINTAINER] = "lru_maintainer",
+        [HOT_LRU_PCT] = "hot_lru_pct",
+        [WARM_LRU_PCT] = "warm_lru_pct",
         NULL
     };
 
@@ -5424,6 +5433,28 @@ int main (int argc, char **argv) {
                     return 1;
                 }
                 break;
+            case HOT_LRU_PCT:
+                if (subopts_value == NULL) {
+                    fprintf(stderr, "Missing hot_lru_pct argument\n");
+                    return 1;
+                };
+                settings.hot_lru_pct = atoi(subopts_value);
+                if (settings.hot_lru_pct < 1 || settings.hot_lru_pct >= 80) {
+                    fprintf(stderr, "hot_lru_pct must be > 1 and < 80\n");
+                    return 1;
+                }
+                break;
+            case WARM_LRU_PCT:
+                if (subopts_value == NULL) {
+                    fprintf(stderr, "Missing warm_lru_pct argument\n");
+                    return 1;
+                };
+                settings.warm_lru_pct = atoi(subopts_value);
+                if (settings.warm_lru_pct < 1 || settings.warm_lru_pct >= 80) {
+                    fprintf(stderr, "warm_lru_pct must be > 1 and < 80\n");
+                    return 1;
+                }
+                break;
             default:
                 printf("Illegal suboption \"%s\"\n", subopts_value);
                 return 1;
@@ -5437,6 +5468,11 @@ int main (int argc, char **argv) {
         }
     }
 
+    if (settings.lru_maintainer_thread && settings.hot_lru_pct + settings.warm_lru_pct > 80) {
+        fprintf(stderr, "hot_lru_pct + warm_lru_pct cannot be more than 80%% combined\n");
+        exit(EX_USAGE);
+    }
+
     if (hash_init(hash_type) != 0) {
         fprintf(stderr, "Failed to initialize hash_algorithm!\n");
         exit(EX_USAGE);

memcached.h

@@ -332,6 +332,8 @@ struct settings {
     char *hash_algorithm;     /* Hash algorithm in use */
     int lru_crawler_sleep;  /* Microsecond sleep between items */
     uint32_t lru_crawler_tocrawl; /* Number of items to crawl per run */
+    int hot_lru_pct; /* percentage of slab space for HOT_LRU */
+    int warm_lru_pct; /* percentage of slab space for WARM_LRU */
 };
 
 extern struct stats stats;

t/binary.t

@@ -2,7 +2,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 3615;
+use Test::More tests => 3624;
 use FindBin qw($Bin);
 use lib "$Bin/lib";
 use MemcachedTest;