From: Jeff Moyer <jmoyer@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
Linux Memory Management List <linux-mm@kvack.org>,
<linux-fsdevel@vger.kernel.org>,
Li Shaohua <shaohua.li@intel.com>,
Clemens Ladisch <clemens@ladisch.de>,
Jens Axboe <jens.axboe@oracle.com>,
Rik van Riel <riel@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH 1/8] block: limit default readahead size for small devices
Date: Tue, 22 Nov 2011 09:23:05 -0500 [thread overview]
Message-ID: <x49wras44om.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20111121145247.0e37dc36.akpm@linux-foundation.org> (Andrew Morton's message of "Mon, 21 Nov 2011 14:52:47 -0800")
Andrew Morton <akpm@linux-foundation.org> writes:
> In a better world, userspace would run a
> work-out-what-readahead-size-to-use script each time a distro is
> installed and when new storage devices are added/detected. Userspace
> would then remember that readahead size for subsequent bootups.
I'd be interested to hear what factors you think should be taken into
account by such a script. I agree that there are certain things, like
timing of reads of different sizes, or heuristics based on the size of
installed memory, which could contribute to the default readahead size.
However, other things, like memory pressure while running the desired
workload, can't really be measured by an installer or one-time script.
> In the real world, we shovel guaranteed-to-be-wrong guesswork into the
> kernel and everyone just uses the results. Sigh.
I'm not sure a userspace tool is the panacea you paint. However, if you
can provide some guidance on what you think could make things better,
I'm happy to give it a go.
Cheers,
Jeff
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next prev parent reply other threads:[~2011-11-22 14:23 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 [this message]
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
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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