BGREWRITEAOF used up 2x used_memory but should not

[rr Feng]

I have a redis instance on a 16GB Linux server，and info memory says:

# Memory

used_memory:6886805512

used_memory_human:6.41G

used_memory_rss:8742027264

used_memory_peak:8470300536

used_memory_peak_human:7.89G

used_memory_lua:36864

mem_fragmentation_ratio:1.27

mem_allocator:jemalloc-3.6.0

and the log:

[1524] 13 Mar 03:00:01.636 * Background append only file rewriting started by pid 6563

[6563] 13 Mar 03:01:46.309 * SYNC append only file rewrite performed

[6563] 13 Mar 03:01:46.318 * AOF rewrite: 7590 MB of memory used by copy-on-write

[1524] 13 Mar 03:01:46.431 * Background AOF rewrite terminated with success

[1524] 13 Mar 03:01:46.433 * Parent diff successfully flushed to the rewritten AOF (2801268 bytes)

[1524] 13 Mar 03:01:46.434 * Background AOF rewrite finished successfully

[1524] 14 Mar 03:00:01.912 # Can't rewrite append only file in background: fork: Cannot allocate memory

[1524] 15 Mar 03:00:01.773 # Can't rewrite append only file in background: fork: Cannot allocate memory

[1524] 16 Mar 03:00:01.676 * Background append only file rewriting started by pid 24154

[1524] 16 Mar 03:00:34.719 # Background AOF rewrite terminated by signal 9

I set save off, and appendonly on, but not auto-rewrite-aof. when the ops is lowest of the day(3:00 am) I run a script to call bgrewriteaof.

"Parent diff successfully flushed to the rewritten AOF (2801268 bytes)" indicates that not many write operations on the rewrite(Am I right? ).

Nothing else running on this server.

Why OOM kill?

Thanks! 

[Tuco]

what is the output of  "cat /proc/sys/vm/overcommit_memory".

If it is 0, you need to run, "echo 1 > cat /proc/sys/vm/overcommit_memory". 

The details are here