memory fragmentation ratio in INFO output

src/config.h

@@ -21,6 +21,11 @@
 #define redis_stat stat
 #endif
 
+/* test for proc filesystem */
+#ifdef __linux__
+#define HAVE_PROCFS 1
+#endif
+
 /* test for backtrace() */
 #if defined(__APPLE__) || defined(__linux__)
 #define HAVE_BACKTRACE 1

src/redis.c

@@ -1166,6 +1166,7 @@ sds genRedisInfoString(void) {
         "blocked_clients:%d\r\n"
         "used_memory:%zu\r\n"
         "used_memory_human:%s\r\n"
+        "mem_fragmentation_ratio:%.2f\r\n"
         "changes_since_last_save:%lld\r\n"
         "bgsave_in_progress:%d\r\n"
         "last_save_time:%ld\r\n"
@@ -1192,6 +1193,7 @@ sds genRedisInfoString(void) {
         server.blpop_blocked_clients,
         zmalloc_used_memory(),
         hmem,
+        zmalloc_get_fragmentation_ratio(),
         server.dirty,
         server.bgsavechildpid != -1,
         server.lastsave,

src/zmalloc.c

@@ -32,6 +32,10 @@
 #include <stdlib.h>
 #include <string.h>
 #include <pthread.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include "config.h"
 
 #if defined(__sun)
@@ -170,3 +174,41 @@ size_t zmalloc_used_memory(void) {
 void zmalloc_enable_thread_safeness(void) {
     zmalloc_thread_safe = 1;
 }
+
+/* Fragmentation = RSS / allocated-bytes */
+float zmalloc_get_fragmentation_ratio(void) {
+#ifdef HAVE_PROCFS
+    size_t allocated = zmalloc_used_memory();
+    int page = sysconf(_SC_PAGESIZE);
+    size_t rss;
+    char buf[4096];
+    char filename[256];
+    int fd, count;
+    char *p, *x;
+
+    snprintf(filename,256,"/proc/%d/stat",getpid());
+    if ((fd = open(filename,O_RDONLY)) == -1) return 0;
+    if (read(fd,buf,4096) <= 0) {
+        close(fd);
+        return 0;
+    }
+    close(fd);
+
+    p = buf;
+    count = 23; /* RSS is the 24th field in /proc/<pid>/stat */
+    while(p && count--) {
+        p = strchr(p,' ');
+        if (p) p++;
+    }
+    if (!p) return 0;
+    x = strchr(p,' ');
+    if (!x) return 0;
+    *x = '\0';
+
+    rss = strtoll(p,NULL,10);
+    rss *= page;
+    return (float)rss/allocated;
+#else
+    return 0;
+#endif
+}

src/zmalloc.h

@@ -38,5 +38,6 @@ void zfree(void *ptr);
 char *zstrdup(const char *s);
 size_t zmalloc_used_memory(void);
 void zmalloc_enable_thread_safeness(void);
+float zmalloc_get_fragmentation_ratio(void);
 
 #endif /* _ZMALLOC_H */