Date: Thu, 24 Jun 2004 11:16:37 -0300
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: William Lee Irwin III <wli@holomorphy.com>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [oom]: [0/4] fix OOM deadlock running OAST
Message-ID: <20040624141637.GA20702@logos.cnet>
References: <0406231407.HbLbJbXaHbKbWa5aJb1a4aKb0a3aKb1a0a2aMbMbYa3aLbMb3aJbWaJbXaMbLb1a342@holomorphy.com> <20040623151659.70333c6d.akpm@osdl.org> <20040623223146.GG1552@holomorphy.com> <20040623153758.40e3a865.akpm@osdl.org> <20040623230730.GJ1552@holomorphy.com> <20040623163819.013c8585.akpm@osdl.org> <20040624000308.GK1552@holomorphy.com> <20040623171818.39b73d52.akpm@osdl.org> <20040624002651.GL1552@holomorphy.com>
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On Wed, Jun 23, 2004 at 05:26:51PM -0700, William Lee Irwin III wrote:
> William Lee Irwin III <wli@holomorphy.com> wrote:
> >> It's a
> >> judgment call as to whether it's beneficial in general, as it does
> >> insulate userspace somewhat from needing to wait for slow IO being the
> >> ostensible cause of the allocation failure.
> 
> On Wed, Jun 23, 2004 at 05:18:18PM -0700, Andrew Morton wrote:
> > mm...  I can only see that happening if the IO system is retiring write
> > requests at much less than 10/sec, which seems unlikely.  Still, that can
> > be tuned around.
> 
> Then it sounds like the smaller fix below may be better for you.
> 
> 
> William Lee Irwin III <wli@holomorphy.com> wrote:
> >> RedHat vendor kernels have removed the check entirely
> 
> On Wed, Jun 23, 2004 at 05:18:18PM -0700, Andrew Morton wrote:
> > When telling us this sort of thing, please always specify the kernel version.
> > I assume you're referring to a 2.6 kernel?  If so, some thwapping might be
> > in order.
> 
> No, RHEL3. I'm not aware of any mm/oom_kill.c changes in any of the
> Fedora snapshots.
> 
> 
> -- wli
> 
> During stress testing at Oracle to determine the maximum number of
> clients 2.6 can service, it was discovered that the failure mode of
> excessive numbers of clients was kernel deadlock. The following patch
> removes the check if (nr_swap_pages > 0) from out_of_memory() as this
> heuristic fails to detect memory exhaustion due to pinned allocations,
> directly causing the aforementioned deadlock.
> 
> 
> ===== mm/oom_kill.c 1.26 vs edited =====
> --- 1.26/mm/oom_kill.c	Thu Jun  3 01:46:39 2004
> +++ edited/mm/oom_kill.c	Wed Jun 23 17:22:22 2004
> @@ -230,12 +230,6 @@
>  	static unsigned long first, last, count, lastkill;
>  	unsigned long now, since;
>  
> -	/*
> -	 * Enough swap space left?  Not OOM.
> -	 */
> -	if (nr_swap_pages > 0)
> -		return;
> -
>  	spin_lock(&oom_lock);
>  	now = jiffies;
>  	since = now - last;

Removing the check on v2.4 based kernels will trigger the OOM killer
too soon for a lot of cases, I'm pretty sure.
-
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