On 12/01/2017 05:35 AM, Thomas Munro wrote:
>> since it also
>> supports "transparent" hugepages.
> Hmm. Yeah, it does, but apparently it's not so transparent.
+1. We saw performance drop with transparent_hugepage enabled on server with
more than 256GB RAM. Access to the cache where slow down when kernel try to
defragment pages.
When that happens, we saw the function isolate_freepages_block appearing in most
consuming function with perf top.
Thanks to Marc Cousin analysis, putting "madvise" to
/sys/kernel/mm/transparent_hugepage/enabled solved the problem. He also notice
that THP only works for "anonymous memory mappings"[1] (shared_buffers are not
anonymous).
1: https://www.kernel.org/doc/Documentation/vm/transhuge.txt
Regards,
--
Adrien NAYRAT
