netdev - Re: [PATCH] mm: do not print backtraces on GFP

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Date:	Tue, 21 Sep 2010 19:00:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] mm: do not print backtraces on GFP_ATOMIC failures

Le mardi 21 septembre 2010 à 09:46 -0700, Andrew Morton a écrit :
> On Tue, 21 Sep 2010 12:18:18 -0400 Rik van Riel <riel@...hat.com> wrote:
> 
> > Atomic allocations cannot fall back to the page eviction code
> > and are expected to fail.  In fact, in some network intensive
> > workloads, it is common to experience hundreds of GFP_ATOMIC
> > allocation failures.
> > 
> > Printing out a backtrace for every one of those expected
> > allocation failures accomplishes nothing good. At multi-gigabit
> > network speeds with jumbo frames, a burst of allocation failure
> > backtraces could even slow down the system.
> > 
> > We're better off not printing out backtraces on GFP_ATOMIC
> > allocation failures.
> > 
> > Signed-off-by: Rik van Riel <riel@...hat.com>
> > 
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 975609c..5a0bddb 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -72,7 +72,7 @@ struct vm_area_struct;
> >  /* This equals 0, but use constants in case they ever change */
> >  #define GFP_NOWAIT	(GFP_ATOMIC & ~__GFP_HIGH)
> >  /* GFP_ATOMIC means both !wait (__GFP_WAIT not set) and use emergency pool */
> > -#define GFP_ATOMIC	(__GFP_HIGH)
> > +#define GFP_ATOMIC	(__GFP_HIGH | __GFP_NOWARN)
> >  #define GFP_NOIO	(__GFP_WAIT)
> >  #define GFP_NOFS	(__GFP_WAIT | __GFP_IO)
> >  #define GFP_KERNEL	(__GFP_WAIT | __GFP_IO | __GFP_FS)
> 
> A much finer-tuned implementation would be to add __GFP_NOWARN just to
> the networking call sites.  I asked about this in June and it got
> nixed:
> 
> http://www.spinics.net/lists/netdev/msg131965.html
> --

Yes, I remember this particular report was useful to find and correct a
bug.

I dont know what to say.

Being silent or verbose, it really depends on the context ?



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