From: Linus Torvalds <torvalds@linux-foundation.org>
To: Olivier Galibert <galibert@pobox.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <jens.axboe@oracle.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 10/11] readahead: dont do start-of-file readahead after lseek()
Date: Tue, 2 Feb 2010 10:40:41 -0800 (PST) [thread overview]
Message-ID: <alpine.LFD.2.00.1002021037110.3664@localhost.localdomain> (raw)
In-Reply-To: <20100202181321.GB75577@dspnet.fr.eu.org>
On Tue, 2 Feb 2010, Olivier Galibert wrote:
>
> Wouldn't that trigger on lseeks to end of file to get the size?
Well, you'd only ever do that with a raw block device, no (if even that:
more "raw block device" tools just use the BLKSIZE64 ioctl etc)? Any sane
regular file accessor will do 'fstat()' instead.
And do we care about startup speed of ramping up read-ahead from the
beginning? In fact, the problem case that caused this was literally
'blkid' on a block device - and the fact that the kernel tried to
read-ahead TOO MUCh rather than too little.
If somebody is really doing lots of serial reading, the read-ahead code
will figure it out very quickly. The case this worries about is just the
_first_ read, where the question is one of "do we think it might be
seeking around, or does it look like the user is going to just read the
whole thing"?
IOW, if you start off with a SEEK_END, I think it's reasonable to expect
it to _not_ read the whole thing.
Linus
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next prev parent reply other threads:[~2010-02-02 18:40 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-02 15:28 [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead Wu Fengguang
2010-02-02 15:28 ` [PATCH 01/11] readahead: limit readahead size for small devices Wu Fengguang
2010-02-02 19:38 ` Jens Axboe
2010-02-03 6:13 ` Wu Fengguang
2010-02-03 8:23 ` Jens Axboe
2010-02-04 8:24 ` Clemens Ladisch
2010-02-04 13:00 ` Wu Fengguang
2010-02-02 15:28 ` [PATCH 02/11] readahead: bump up the default readahead size Wu Fengguang
2010-02-02 15:28 ` [PATCH 03/11] readahead: introduce {MAX|MIN}_READAHEAD_PAGES macros for ease of use Wu Fengguang
2010-02-02 15:28 ` [PATCH 04/11] readahead: replace ra->mmap_miss with ra->ra_flags Wu Fengguang
2010-02-02 15:28 ` [PATCH 05/11] readahead: retain inactive lru pages to be accessed soon Wu Fengguang
2010-02-02 15:28 ` [PATCH 06/11] readahead: thrashing safe context readahead Wu Fengguang
2010-02-02 15:28 ` [PATCH 07/11] readahead: record readahead patterns Wu Fengguang
2010-02-02 15:28 ` [PATCH 08/11] readahead: add tracing event Wu Fengguang
2010-02-12 16:19 ` Steven Rostedt
2010-02-14 3:56 ` Wu Fengguang
2010-02-02 15:28 ` [PATCH 09/11] readahead: add /debug/readahead/stats Wu Fengguang
2010-02-02 15:28 ` [PATCH 10/11] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
2010-02-02 17:39 ` Linus Torvalds
2010-02-02 18:13 ` Olivier Galibert
2010-02-02 18:40 ` Linus Torvalds [this message]
2010-02-02 18:48 ` Olivier Galibert
2010-02-02 19:14 ` Linus Torvalds
2010-02-02 19:59 ` david
2010-02-02 20:22 ` Linus Torvalds
2010-02-02 15:28 ` [PATCH 11/11] radixtree: speed up next/prev hole search Wu Fengguang
2010-02-02 22:38 ` [PATCH 00/11] [RFC] 512K readahead size with thrashing safe readahead Vivek Goyal
2010-02-02 23:17 ` Vivek Goyal
2010-02-03 6:27 ` Wu Fengguang
2010-02-03 15:24 ` Vivek Goyal
2010-02-03 15:58 ` Vivek Goyal
2010-02-04 13:21 ` Wu Fengguang
2010-02-04 15:52 ` Vivek Goyal
2010-02-04 13:44 ` Wu Fengguang
-- strict thread matches above, loose matches on Subject: below --
2010-02-07 4:10 [PATCH 00/11] " Wu Fengguang
2010-02-07 4:10 ` [PATCH 10/11] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
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