From: Wu Fengguang <fengguang.wu@intel.com>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <andi@firstfloor.org>,
"Li, Shaohua" <shaohua.li@intel.com>,
Linux Memory Management List <linux-mm@kvack.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 8/9] readahead: basic support for backwards prefetching
Date: Wed, 30 Nov 2011 08:37:16 +0800 [thread overview]
Message-ID: <20111130003716.GA11147@localhost> (raw)
In-Reply-To: <20111129153552.GP5635@quack.suse.cz>
(snip)
> > @@ -676,6 +677,20 @@ ondemand_readahead(struct address_space
> > }
> >
> > /*
> > + * backwards reading
> > + */
> > + if (offset < ra->start && offset + req_size >= ra->start) {
> > + ra->pattern = RA_PATTERN_BACKWARDS;
> > + ra->size = get_next_ra_size(ra, max);
> > + max = ra->start;
> > + if (ra->size > max)
> > + ra->size = max;
> > + ra->async_size = 0;
> > + ra->start -= ra->size;
> IMHO much more obvious way to write this is:
> ra->size = get_next_ra_size(ra, max);
> if (ra->size > ra->start) {
> ra->size = ra->start;
> ra->start = 0;
> } else
> ra->start -= ra->size;
Good idea! Here is the updated code:
/*
* backwards reading
*/
if (offset < ra->start && offset + req_size >= ra->start) {
ra->pattern = RA_PATTERN_BACKWARDS;
ra->size = get_next_ra_size(ra, max);
if (ra->size > ra->start) {
/*
* ra->start may be concurrently set to some huge
* value, the min() at least avoids submitting huge IO
* in this race condition
*/
ra->size = min(ra->start, max);
ra->start = 0;
} else
ra->start -= ra->size;
ra->async_size = 0;
goto readit;
}
Thanks,
Fengguang
next prev parent reply other threads:[~2011-11-30 0:37 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-29 13:09 [PATCH 0/9] readahead stats/tracing, backwards prefetching and more (v2) Wu Fengguang
2011-11-29 13:09 ` [PATCH 1/9] block: limit default readahead size for small devices Wu Fengguang
2011-11-29 13:09 ` [PATCH 2/9] readahead: snap readahead request to EOF Wu Fengguang
2011-11-29 14:29 ` Jan Kara
2011-11-30 1:06 ` Wu Fengguang
2011-11-30 11:37 ` Jan Kara
2011-11-30 12:06 ` Wu Fengguang
2011-11-29 13:09 ` [PATCH 3/9] readahead: record readahead patterns Wu Fengguang
2011-11-29 14:40 ` Jan Kara
2011-11-29 17:57 ` Andi Kleen
2011-11-30 1:18 ` Wu Fengguang
2011-12-15 8:55 ` [PATCH] proc: show readahead state in fdinfo Wu Fengguang
2011-12-15 9:49 ` Ingo Molnar
2011-11-29 13:09 ` [PATCH 4/9] readahead: tag mmap page fault call sites Wu Fengguang
2011-11-29 14:41 ` Jan Kara
2011-11-29 13:09 ` [PATCH 5/9] readahead: tag metadata " Wu Fengguang
2011-11-29 14:45 ` Jan Kara
2011-11-29 13:09 ` [PATCH 6/9] readahead: add /debug/readahead/stats Wu Fengguang
2011-11-29 15:21 ` Jan Kara
2011-11-30 0:44 ` Wu Fengguang
2011-12-14 6:36 ` Wu Fengguang
2011-12-19 16:32 ` Jan Kara
2011-12-21 1:29 ` Wu Fengguang
2011-12-21 4:06 ` Dave Chinner
2011-12-23 3:33 ` Wu Fengguang
2011-12-23 11:16 ` Jan Kara
2011-11-29 13:09 ` [PATCH 7/9] readahead: add vfs/readahead tracing event Wu Fengguang
2011-11-29 15:22 ` Jan Kara
2011-11-30 0:42 ` Wu Fengguang
2011-11-30 11:44 ` Jan Kara
2011-11-30 12:06 ` Wu Fengguang
2011-12-06 15:30 ` Christoph Hellwig
2011-12-07 9:18 ` Wu Fengguang
2011-12-08 9:03 ` [PATCH] writeback: show writeback reason with __print_symbolic Wu Fengguang
2011-11-29 13:09 ` [PATCH 8/9] readahead: basic support for backwards prefetching Wu Fengguang
2011-11-29 15:35 ` Jan Kara
2011-11-29 16:37 ` Pádraig Brady
2011-11-30 0:24 ` Wu Fengguang
2011-11-30 0:37 ` Wu Fengguang [this message]
2011-11-30 11:21 ` Jan Kara
2011-11-29 13:09 ` [PATCH 9/9] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
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