linux-kernel - Re: [PATCH for 2.6.18] [8/8] MM: Remove rogue readahead printk

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Message-ID: <5c49b0ed0607291804j28193807t83d8237cad8d5ecd@mail.gmail.com>
Date:	Sat, 29 Jul 2006 18:04:18 -0700
From:	"Nate Diller" <nate.diller@...il.com>
To:	"Trond Myklebust" <trond.myklebust@....uio.no>
Cc:	"Andi Kleen" <ak@...e.de>, torvalds@...l.org, discuss@...-64.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH for 2.6.18] [8/8] MM: Remove rogue readahead printk

On 7/29/06, Trond Myklebust <trond.myklebust@....uio.no> wrote:
> On Sat, 2006-07-29 at 21:42 +0200, Andi Kleen wrote:
> > For some reason it triggers always with NFS root and spams the kernel
> > logs of my nfs root boxes a lot.
> >
> > Cc: trond.myklebust@....uio.no
> > Signed-off-by: Andi Kleen <ak@...e.de>
>
> Big ACK! I never really understood why we needed this printk, and yes,
> it does spam the syslog heavily on all NFS clients...

not an NFS user, but it seems like this is indicating an actual
performance problem.  the printk was introduced by an attempt to
reduce retries after -EIO on scratched CDs/DVDs, and is intended to
curb pathological behavior when one disk sector consitently cannot be
read.

for some reason (maybe just busy networks, dunno), you're getting I/O
errors on NFS, and the readahead window is being reduced.  IMO, the
proper behavior in this case would be to keep it large, or even
increase it, since that would enable the network to more efficiently
transfer data.

of course, it could be that some quirk of the NFS client VFS interface
causes "spurious" -EIO returns.  either way, i'd rather see it fixed
rather than the printk removed, since it is useful to point out that
some performance degradation is occuring.

NATE
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