linux-kernel - Re: [RFC] Reproducible OOM with partial workaround

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20130111123149.c3232a96.akpm@linux-foundation.org>
Date:	Fri, 11 Jan 2013 12:31:49 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	paul.szabo@...ney.edu.au
Cc:	695182@...s.debian.org, dave@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC] Reproducible OOM with partial workaround

On Fri, 11 Jan 2013 22:51:35 +1100
paul.szabo@...ney.edu.au wrote:

> Dear Andrew,
> 
> > Check /proc/slabinfo, see if all your lowmem got eaten up by buffer_heads.
> 
> Please see below: I do not know what any of that means. This machine has
> been running just fine, with all my users logging in here via XDMCP from
> X-terminals, dozens logged in simultaneously. (But, I think I could make
> it go OOM with more processes or logins.)

I'm counting 107MB in slab there.  Was this dump taken when the system
was at or near oom?

Please send a copy of the oom-killer kernel message dump, if you still
have one.

> > If so, you *may* be able to work around this by setting
> > /proc/sys/vm/dirty_ratio really low, so the system keeps a minimum
> > amount of dirty pagecache around.  Then, with luck, if we haven't
> > broken the buffer_heads_over_limit logic it in the past decade (we
> > probably have), the VM should be able to reclaim those buffer_heads.
> 
> I tried setting dirty_ratio to "funny" values, that did not seem to
> help.

Did you try setting it as low as possible?

> Did you notice my patch about bdi_position_ratio(), how it was
> plain wrong half the time (for negative x)? 

Nope, please resend.

> Anyway that did not help.
> 
> > Alternatively, use a filesystem which doesn't attach buffer_heads to
> > dirty pages.  xfs or btrfs, perhaps.
> 
> Seems there is also a problem not related to filesystem... or rather,
> the essence does not seem to be filesystem or caches. The filesystem
> thing now seems OK with my patch doing drop_caches.

hm, if doing a regular drop_caches fixes things then that implies the
problem is not with dirty pagecache.  Odd.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/