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

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Date:	Fri, 19 Jun 2009 15:37:17 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

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.

That was possible because of the page allocation failure messages that 
were noticed by the user; without this evidence, the only symptom would 
have been extremely slow I/O over nfs.  This could involve any number of 
subsystems and I doubt the first reaction would have been to enable 
CONFIG_DEBUG_VM.
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