From: Andrew Morton <akpm@osdl.org>
To: Ram Pai <linuxram@us.ibm.com>
Cc: miklos@szeredi.hu, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix readahead breakage for sequential after random reads
Date: Mon, 26 Jul 2004 17:08:43 -0700 [thread overview]
Message-ID: <20040726170843.3fe5615c.akpm@osdl.org> (raw)
In-Reply-To: <1090886218.8416.3.camel@dyn319181.beaverton.ibm.com>
Ram Pai <linuxram@us.ibm.com> wrote:
>
> Andrew,
> Yes the patch fixes a valid bug.
>
Please don't top-post :(
> RP
>
> On Mon, 2004-07-26 at 16:29, Andrew Morton wrote:
> > Miklos Szeredi <miklos@szeredi.hu> wrote:
> > >
> > > Current readahead logic is broken when a random read pattern is
> > > followed by a long sequential read. The cause is that on a window
> > > miss ra->next_size is set to ra->average, but ra->average is only
> > > updated at the end of a sequence, so window size will remain 1 until
> > > the end of the sequential read.
> > >
> > > This patch fixes this by taking the current sequence length into
> > > account (code taken from towards end of page_cache_readahead()), and
> > > also setting ra->average to a decent value in handle_ra_miss() when
> > > sequential access is detected.
> >
> > Thanks. Do you have any performance testing results from this patch?
> >
> Ram Pai <linuxram@us.ibm.com> wrote:
>
> Andrew,
> Yes the patch fixes a valid bug.
Fine, but the readahead code is performance-sensitive, and it takes quite
some time for any regressions to be discovered. So I'm going to need to
either sit on this patch for a very long time, or extensively test it
myself, or await convincing test results from someone else.
Can you help with that?
next prev parent reply other threads:[~2004-07-27 0:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-18 22:30 [PATCH] fix readahead breakage for sequential after random reads Miklos Szeredi
2004-07-26 23:29 ` Andrew Morton
2004-07-26 23:56 ` Ram Pai
2004-07-27 0:08 ` Andrew Morton [this message]
2004-07-27 4:18 ` Ram Pai
2004-07-27 7:40 ` Miklos Szeredi
2004-07-27 15:34 ` Ram Pai
2004-08-04 17:38 ` Ram Pai
2004-08-04 19:39 ` Shane Shrybman
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