linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Wu Fengguang <fengguang.wu@intel.com>
To: "Pádraig Brady" <P@draigBrady.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 08:24:25 +0800	[thread overview]
Message-ID: <20111130002425.GA8734@localhost> (raw)
In-Reply-To: <4ED50A63.1010805@draigBrady.com>

On Wed, Nov 30, 2011 at 12:37:55AM +0800, Pádraig Brady wrote:
> On 11/29/2011 03:35 PM, Jan Kara wrote:
> >   Someone already mentioned this earlier and I don't think I've seen a
> > response: Do you have a realistic usecase for this? I don't think I've ever
> > seen an application reading file backwards...
> 
> tac, tail -n$large, ...

Indeed!
             tac-4425  [000] 73358.419777: readahead: readahead-random(dev=0:16, ino=1548445, req=750+1, ra=750+1-0, async=0) = 1
             tac-4425  [004] 73358.442030: readahead: readahead-backwards(dev=0:16, ino=1548445, req=748+2, ra=746+5-0, async=0) = 4
             tac-4425  [004] 73358.443312: readahead: readahead-backwards(dev=0:16, ino=1548445, req=744+2, ra=726+25-0, async=0) = 20

            tail-4369  [000] 72633.696307: readahead: readahead-random(dev=0:16, ino=1548450, req=750+1, ra=750+1-0, async=0) = 1
            tail-4369  [004] 72634.042106: readahead: readahead-backwards(dev=0:16, ino=1548450, req=748+2, ra=746+5-0, async=0) = 4
            tail-4369  [004] 72634.043231: readahead: readahead-backwards(dev=0:16, ino=1548450, req=744+2, ra=726+25-0, async=0) = 20
            tail-4369  [004] 72634.176216: readahead: readahead-backwards(dev=0:16, ino=1548450, req=724+2, ra=626+125-0, async=0) = 100

However I see the readahead requests always be snapped to EOF.

So it's obvious the "snap to EOF" logic need some limiting based on
max readahead size.

Thanks,
Fengguang

  reply	other threads:[~2011-11-30  0:24 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 [this message]
2011-11-30  0:37     ` Wu Fengguang
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

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=20111130002425.GA8734@localhost \
    --to=fengguang.wu@intel.com \
    --cc=P@draigBrady.com \
    --cc=akpm@linux-foundation.org \
    --cc=andi@firstfloor.org \
    --cc=jack@suse.cz \
    --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).