[Bug libc/20425] unbalanced and poor utilization of memory in glibc arenas may cause memory bloat and subsequent OOM

["sumeet.keswani at hpe dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20425

--- Comment #17 from Sumeet Keswani <sumeet.keswani at hpe dot com> ---
(In reply to Florian Weimer from comment #16)
> (In reply to Sumeet Keswani from comment #15)
> > Created attachment 9446 [details]
> > reproducer done on glibc-2.22
> > 
> > Attached reproducer was done on glibc-2.22
> > It demonstrates the increase in RSS memory.
> 
> Can you clarify what your concern is?
> 
> The bug started with an observed unevenness in the arena selection.  Do you
> still see this as a problem, or are you solely concerned about RSS usage?
> 
> > There are some output files in the tarball that show a local run using the
> > code provided on the following machine config
> 
> Thanks, I have found a remarkably similar machine (but naturally, it's not
> running under Xen).

sorry for the long response...

Our concern is the perpetually increasing RSS, which ultimately causes a OOM
kill. This is the bottom line. We see this problem with versions/builds of
glibc which have the fix for Bug 19048. Consequently we believe that this
problem has been exposed by or is related to fix for 19048.

In between glibc 2.12.1-166 and 2.12.1.192 we can see "unbalanced and poor
utilization" of the arenas which cause memory significant memory bloat and OOM
kill.

Subsequently we ran the reproducer on glibc-2.22. Here we don’t see this
"unbalanced and poor utilization", however arenas grows (leak) with each
iteration which will ultimately result in an OOM.


So yes, I am happy to fork this bug into two. 
One for the 2.12 stream where we can see unbalanced use of arenas is apparent.
and another for 2.22 where arenas grow steadily.

Both result in OOM.

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