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/defrag.c

@@ -700,18 +700,9 @@ void defragDictBucketCallback(void *privdata, dictEntry **bucketref) {
  * or not, a false detection can cause the defragmenter to waste a lot of CPU
  * without the possibility of getting any results. */
 float getAllocatorFragmentation(size_t *out_frag_bytes) {
-    size_t epoch = 1, allocated = 0, resident = 0, active = 0, sz = sizeof(size_t);
-    /* 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);
+    size_t resident = server.cron_malloc_stats.allocator_resident;
+    size_t active = server.cron_malloc_stats.allocator_active;
+    size_t allocated = server.cron_malloc_stats.allocator_allocated;
     float frag_pct = ((float)active / allocated)*100 - 100;
     size_t frag_bytes = active - allocated;
     float rss_pct = ((float)resident / allocated)*100 - 100;