Adding real allocator fragmentation to INFO and MEMORY command + active defrag test

other fixes / improvements:
- LUA script memory isn't taken from zmalloc (taken from libc malloc)
  so it can cause high fragmentation ratio to be displayed (which is false)
- there was a problem with "fragmentation" info being calculated from
  RSS and used_memory sampled at different times (now sampling them together)

other details:
- adding a few more allocator info fields to INFO and MEMORY commands
- improve defrag test to measure defrag latency of big keys
- increasing the accuracy of the defrag test (by looking at real grag info)
  this way we can use an even lower threshold and still avoid false positives
- keep the old (total) "fragmentation" field unchanged, but add new ones for spcific things
- add these the MEMORY DOCTOR command
- deduct LUA memory from the rss in case of non jemalloc allocator (one for which we don't "allocator active/used")
- reduce sampling rate of the rss and allocator info

src/zmalloc.c

@@ -297,10 +297,33 @@ size_t zmalloc_get_rss(void) {
 }
 #endif
 
-/* Fragmentation = RSS / allocated-bytes */
-float zmalloc_get_fragmentation_ratio(size_t rss) {
-    return (float)rss/zmalloc_used_memory();
+#if defined(USE_JEMALLOC)
+int zmalloc_get_allocator_info(size_t *allocated,
+                               size_t *active,
+                               size_t *resident) {
+    size_t epoch = 1, sz = sizeof(size_t);
+    *allocated = *resident = *active = 0;
+    /* Update the statistics cached by mallctl. */
+    je_mallctl("epoch", &epoch, &sz, &epoch, sz);
+    /* Unlike RSS, this does not include RSS from shared libraries and other non
+     * heap mappings. */
+    je_mallctl("stats.resident", resident, &sz, NULL, 0);
+    /* Unlike resident, this doesn't not include the pages jemalloc reserves
+     * for re-use (purge will clean that). */
+    je_mallctl("stats.active", active, &sz, NULL, 0);
+    /* Unlike zmalloc_used_memory, this matches the stats.resident by taking
+     * into account all allocations done by this process (not only zmalloc). */
+    je_mallctl("stats.allocated", allocated, &sz, NULL, 0);
+    return 1;
 }
+#else
+int zmalloc_get_allocator_info(size_t *allocated,
+                               size_t *active,
+                               size_t *resident) {
+    *allocated = *resident = *active = 0;
+    return 1;
+}
+#endif
 
 /* Get the sum of the specified field (converted form kb to bytes) in
  * /proc/self/smaps. The field must be specified with trailing ":" as it