A GNU C Library update

Posted Feb 27, 2015 6:48 UTC (Fri) by rsidd (subscriber, #2582)
In reply to: A GNU C Library update by madscientist
Parent article: A GNU C Library update

Interesting, thanks! But it looks like the problem is fixable in jemalloc, at least for kernel 2.6.38 and later -- basically, jemalloc can explicitly turn off huge page allocations. (There is no later jemalloc release, I don't know if the patch they give has been merged.)

A GNU C Library update

Posted Feb 27, 2015 17:41 UTC (Fri) by madscientist (subscriber, #16861) [Link] (2 responses)

Yeah, I saw that back when it was posted. When we did an experiment with /sys/kernel/mm/transparent_hugepage/enabled value set to "always", which is the default setting on all modern GNU/Linux distros I'm aware of, we still saw AnonHuge pages in the process space even after applying that patch to jemalloc to use MADV_NOHUGEPAGE, unless we set enabled to either madvise or never to disable THP by default.

However, I took a look at the implementation in mm/huge_memory.c and talked with my colleague, and now we wonder if that was just an artifact of some static allocations or something that were not using jemalloc for some reason (honestly I'm not sure how this would happen but...).

I'll try to find some time this weekend to do a deeper test and verify whether RSS vs. jemalloc's HeapActive value is actually diverging (this is the symptom of the problem), rather than just looking at AnonHuge in proc.

A GNU C Library update

Posted Mar 1, 2015 0:28 UTC (Sun) by mathstuf (subscriber, #69389) [Link]

> the default setting on all modern GNU/Linux distros I'm aware of

FWIW, it is madvise on Fedora (Rawhide).

A GNU C Library update

Posted Mar 2, 2015 23:37 UTC (Mon) by Gerardo (subscriber, #37539) [Link]

Also in Debian, here.