From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linux Memory Management List <linux-mm@kvack.org>,
linux-fsdevel@vger.kernel.org, Andi Kleen <andi@firstfloor.org>,
Li Shaohua <shaohua.li@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 7/8] readahead: basic support for backwards prefetching
Date: Tue, 29 Nov 2011 11:08:09 +0800 [thread overview]
Message-ID: <20111129030809.GB19506@localhost> (raw)
In-Reply-To: <20111121153309.d2a410fb.akpm@linux-foundation.org>
On Mon, Nov 21, 2011 at 03:33:09PM -0800, Andrew Morton wrote:
> On Mon, 21 Nov 2011 17:18:26 +0800
> Wu Fengguang <fengguang.wu@intel.com> wrote:
>
> > Add the backwards prefetching feature. It's pretty simple if we don't
> > support async prefetching and interleaved reads.
>
> Well OK, but I wonder how many applications out there read files in
> reverse order. Is it common enough to bother special-casing in the
> kernel like this?
Maybe not so many applications, but sure there are some real cases
somewhere. I remember an IBM paper (that's many years ago, so cannot
recall the exact title) on database shows a graph containing backwards
reading curves among the other ones.
Recently Shaohua even run into a performance regression caused by glibc
optimizing memcpy to access page in reverse order (15, 14, 13, ... 0).
Well this patch may not be the most pertinent fix to that particular
issue. But you see the opportunity such access patterns arise from
surprised areas.
Thanks,
Fengguang
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next prev parent reply other threads:[~2011-11-29 3:08 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-21 9:18 [PATCH 0/8] readahead stats/tracing, backwards prefetching and more Wu Fengguang
2011-11-21 9:18 ` [PATCH 1/8] block: limit default readahead size for small devices Wu Fengguang
2011-11-21 10:00 ` Christoph Hellwig
2011-11-21 11:24 ` Wu Fengguang
2011-11-21 12:47 ` Andi Kleen
2011-11-21 14:46 ` Jeff Moyer
2011-11-21 22:52 ` Andrew Morton
2011-11-22 14:23 ` Jeff Moyer
2011-11-23 12:18 ` Wu Fengguang
2011-11-21 9:18 ` [PATCH 2/8] readahead: make default readahead size a kernel parameter Wu Fengguang
2011-11-21 10:01 ` Christoph Hellwig
2011-11-21 11:35 ` Wu Fengguang
2011-11-24 22:28 ` Jan Kara
2011-11-25 0:36 ` Dave Chinner
2011-11-28 2:39 ` Wu Fengguang
2011-11-30 13:04 ` Christian Ehrhardt
2011-11-30 13:29 ` Wu Fengguang
2011-11-30 16:09 ` Jan Kara
2011-11-21 13:16 ` Namhyung Kim
2011-11-21 13:24 ` Wu Fengguang
2011-11-21 9:18 ` [PATCH 3/8] readahead: replace ra->mmap_miss with ra->ra_flags Wu Fengguang
2011-11-21 11:04 ` Steven Whitehouse
2011-11-21 11:42 ` Wu Fengguang
2011-11-21 23:01 ` Andrew Morton
2011-11-23 12:47 ` Wu Fengguang
2011-11-23 20:31 ` Andrew Morton
2011-11-29 3:42 ` Wu Fengguang
2011-11-21 9:18 ` [PATCH 4/8] readahead: record readahead patterns Wu Fengguang
2011-11-21 23:19 ` Andrew Morton
2011-11-29 2:40 ` Wu Fengguang
2011-11-21 9:18 ` [PATCH 5/8] readahead: add /debug/readahead/stats Wu Fengguang
2011-11-21 14:17 ` Andi Kleen
2011-11-22 14:14 ` Wu Fengguang
2011-11-21 23:29 ` Andrew Morton
2011-11-21 23:32 ` Andi Kleen
2011-11-29 3:23 ` Wu Fengguang
2011-11-29 4:49 ` Andrew Morton
2011-11-29 6:41 ` Wu Fengguang
2011-11-29 12:29 ` Wu Fengguang
2011-11-21 9:18 ` [PATCH 6/8] readahead: add debug tracing event Wu Fengguang
2011-11-21 14:01 ` Steven Rostedt
2011-11-21 9:18 ` [PATCH 7/8] readahead: basic support for backwards prefetching Wu Fengguang
2011-11-21 23:33 ` Andrew Morton
2011-11-29 3:08 ` Wu Fengguang [this message]
2011-11-21 9:18 ` [PATCH 8/8] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
2011-11-21 23:36 ` Andrew Morton
2011-11-22 14:18 ` Wu Fengguang
2011-11-21 9:56 ` [PATCH 0/8] readahead stats/tracing, backwards prefetching and more Christoph Hellwig
2011-11-21 12:00 ` Wu Fengguang
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