From: Jan Kara <jack@suse.cz>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>,
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 12:21:46 +0100 [thread overview]
Message-ID: <20111130112146.GB4541@quack.suse.cz> (raw)
In-Reply-To: <20111130003716.GA11147@localhost>
On Wed 30-11-11 08:37:16, Wu Fengguang wrote:
> (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;
> }
Looks good. You can add:
Acked-by: Jan Kara <jack@suse.cz>
to the patch.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2011-11-30 11:21 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
2011-11-30 11:21 ` Jan Kara [this message]
2011-11-29 13:09 ` [PATCH 9/9] readahead: dont do start-of-file readahead after lseek() Wu Fengguang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20111130112146.GB4541@quack.suse.cz \
--to=jack@suse.cz \
--cc=akpm@linux-foundation.org \
--cc=andi@firstfloor.org \
--cc=fengguang.wu@intel.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=shaohua.li@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).