linux-kernel - Re: [patch] ipv4: don't warn about skb ack allocation failures

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Date:	Fri, 19 Jun 2009 18:28:49 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Rientjes <rientjes@...gle.com>
Cc:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	jpiszcz@...idpixels.com, linux-kernel@...r.kernel.org
Subject: Re: [patch] ipv4: don't warn about skb ack allocation failures

David Rientjes <rientjes@...gle.com> writes:

> On Fri, 19 Jun 2009, Eric W. Biederman wrote:
>
>> But Mr. Reintjes if you really want the traces I can set up 
>> an script to email them to you every time it happens.  Say about
>> 1 a minute from my paltry little farm of machines.
>> 
>
> Perhaps you missed my email where I suggested emitting the page allocation 
> warnings only when CONFIG_DEBUG_VM is enabled.  It's at 
> http://lkml.org/lkml/2009/6/18/355.
>
> We can then keep the __GFP_NOFAIL flag to indicate that the warnings 
> should never be emitted for that allocation, regardless of the .config.
>
> It's funny, though, that the problem that originally started this thread 
> was quickly diagnosed because of these messages.  As far as I know, my 
> suggestion to increase /proc/sys/vm/dirty_background_ratio to kick pdflush 
> earlier has prevented the slab allocation failures and not required 
> delayed acks for nfsd.

increase?

Perhaps then the problem is simply dirty_background_ratio.  Is the vm
not properly autotuning?

With a 50MB/s disk I wonder what the proper window size is.  Several
gigabytes as implied by a 5% or a 10% dirty_background_ratio seems
absurd.  TCP sockets seem to get along fine with even large latencies
and windows measured in megabytes not gigabytes.

This does explain a few things.

Eric
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