From: Fengguang Wu <wfg@mail.ustc.edu.cn>
To: Michael Rubin <mrubin@google.com>
Cc: a.p.zijlstra@chello.nl, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Chris Mason <chris.mason@oracle.com>
Subject: Re: [patch 1/1] Writeback fix for concurrent large and small file writes
Date: Fri, 30 Nov 2007 09:32:59 +0800 [thread overview]
Message-ID: <396386387.18082@ustc.edu.cn> (raw)
Message-ID: <E1IxukV-0003Ns-5C@localhost> (raw)
In-Reply-To: <532480950711291216l181b0bej17db6c42067aa832@mail.gmail.com>
On Thu, Nov 29, 2007 at 12:16:36PM -0800, Michael Rubin wrote:
> Due to my faux pas of top posting (see
> http://www.zip.com.au/~akpm/linux/patches/stuff/top-posting.txt) I am
> resending this email.
>
> On Nov 28, 2007 4:34 PM, Fengguang Wu <wfg@mail.ustc.edu.cn> wrote:
> > Could you demonstrate the situation? Or if I guess it right, could it
> > be fixed by the following patch? (not a nack: If so, your patch could
> > also be considered as a general purpose improvement, instead of a bug
> > fix.)
> >
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 0fca820..62e62e2 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -301,7 +301,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
> > * Someone redirtied the inode while were writing back
> > * the pages.
> > */
> > - redirty_tail(inode);
> > + requeue_io(inode);
> > } else if (atomic_read(&inode->i_count)) {
> > /*
> > * The inode is clean, inuse
> >
>
> By testing the situation I can confirm that the one line patch above
> fixes the problem.
>
> I will continue testing some other cases to see if it cause any other
> issues but I don't expect it to.
One major concern could be whether a continuous writer dirting pages
at the 'right' pace will generate a steady flow of write I/Os which are
_tiny_hence_inefficient_.
I have gathered some timing info about writeback speed in
http://lkml.org/lkml/2007/10/4/468. For ext3, it takes wb_kupdate()
~15ms to submit 4MB. Whereas one disk I/O typically takes ~5ms. So if
there are too many tiny write I/Os, they will simply get delayed and
merged into bigger ones.
So it's not a problem in *theory* :-)
> I will post this change for 2.6.24 and list Feng as author. If that's
> ok with Feng.
Thank you.
> As for the original patch I will resubmit it for 2.6.25 as a general
> purpose improvement.
There are some discussions and patches on inode number based writeback
clustering which you may want to reference/compare with:
http://lkml.org/lkml/2007/8/21/396
http://lkml.org/lkml/2007/8/27/45
Cheers,
Fengguang
next prev parent reply other threads:[~2007-11-30 1:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-28 19:29 [patch 1/1] Writeback fix for concurrent large and small file writes Michael Rubin
[not found] ` <E1IxXMP-0002i8-4S@localhost>
2007-11-29 0:34 ` Fengguang Wu
2007-11-29 19:51 ` Michael Rubin
2007-11-29 20:16 ` Michael Rubin
[not found] ` <E1IxukV-0003Ns-5C@localhost>
2007-11-30 1:32 ` Fengguang Wu [this message]
2007-12-04 9:06 ` Michael Rubin
2007-11-29 2:13 ` Frans Pop
2007-11-29 6:58 ` Michael Rubin
2007-12-11 2:02 Michael Rubin
2007-12-12 20:55 ` Peter Zijlstra
2007-12-12 23:03 ` Michael Rubin
[not found] ` <E1J89kR-0001v3-CJ@localhost>
2007-12-28 7:35 ` Fengguang Wu
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