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Date:	Wed, 16 Jan 2008 11:27:54 -0500
From:	"Mike Snitzer" <snitzer@...il.com>
To:	"Martin Knoblauch" <spamtrap@...bisoft.de>
Cc:	"Fengguang Wu" <wfg@...l.ustc.edu.cn>,
	"Peter Zijlstra" <peterz@...radead.org>, jplatte@...sa.net,
	"Ingo Molnar" <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: Re: regression: 100% io-wait with 2.6.24-rcX

On Jan 16, 2008 9:15 AM, Martin Knoblauch <spamtrap@...bisoft.de> wrote:
> ----- Original Message ----
> > From: Fengguang Wu <wfg@...l.ustc.edu.cn>
> > To: Martin Knoblauch <knobi@...bisoft.de>
> > Cc: Mike Snitzer <snitzer@...il.com>; Peter Zijlstra <peterz@...radead.org>; jplatte@...sa.net; Ingo Molnar <mingo@...e.hu>; linux-kernel@...r.kernel.org; "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>; Linus Torvalds <torvalds@...ux-foundation.org>
> > Sent: Wednesday, January 16, 2008 1:00:04 PM
> > Subject: Re: regression: 100% io-wait with 2.6.24-rcX
> >
>
> > On Wed, Jan 16, 2008 at 01:26:41AM -0800, Martin Knoblauch wrote:
> > > > For those interested in using your writeback improvements in
> > > > production sooner rather than later (primarily with ext3); what
> > > > recommendations do you have?  Just heavily test our own 2.6.24
> > +
> >
>  your
> > > > evolving "close, but not ready for merge" -mm writeback patchset?
> > > >
> > > Hi Fengguang, Mike,
> > >
> > >  I can add myself to Mikes question. It would be good to know
> > a
> >
>  "roadmap" for the writeback changes. Testing 2.6.24-rcX so far has
> > been
> >
>  showing quite nice improvement of the overall writeback situation and
> > it
> >
>  would be sad to see this [partially] gone in 2.6.24-final.
> > Linus
> >
>  apparently already has reverted  "...2250b". I will definitely repeat my
> > tests
> >
>  with -rc8. and report.
> >
> > Thank you, Martin. Can you help test this patch on 2.6.24-rc7?
> > Maybe we can push it to 2.6.24 after your testing.
> >
>
>  Will do tomorrow or friday. Actually a patch against -rc8 would be nicer for me, as I have not looked at -rc7 due to holidays and some of the reported problems with it.

Fengguang's latest writeback patch applies cleanly, builds, boots on 2.6.24-rc8.

I'll be able to share ext3 performance results (relative to 2.6.24-rc7) shortly.

Mike
>
>
> > Fengguang
> > ---
> >  fs/fs-writeback.c         |   17 +++++++++++++++--
> >  include/linux/writeback.h |    1 +
> >  mm/page-writeback.c       |    9 ++++++---
> >  3 files changed, 22 insertions(+), 5 deletions(-)
> >
> > --- linux.orig/fs/fs-writeback.c
> > +++ linux/fs/fs-writeback.c
> > @@ -284,7 +284,16 @@ __sync_single_inode(struct inode *inode,
> >                   * soon as the queue becomes uncongested.
> >                   */
> >                  inode->i_state |= I_DIRTY_PAGES;
> > -                requeue_io(inode);
> > +                if (wbc->nr_to_write <= 0)
> > +                    /*
> > +                     * slice used up: queue for next turn
> > +                     */
> > +                    requeue_io(inode);
> > +                else
> > +                    /*
> > +                     * somehow blocked: retry later
> > +                     */
> > +                    redirty_tail(inode);
> >              } else {
> >                  /*
> >                   * Otherwise fully redirty the inode so that
> > @@ -479,8 +488,12 @@ sync_sb_inodes(struct super_block *sb, s
> >          iput(inode);
> >          cond_resched();
> >          spin_lock(&inode_lock);
> > -        if (wbc->nr_to_write <= 0)
> > +        if (wbc->nr_to_write <= 0) {
> > +            wbc->more_io = 1;
> >              break;
> > +        }
> > +        if (!list_empty(&sb->s_more_io))
> > +            wbc->more_io = 1;
> >      }
> >      return;        /* Leave any unwritten inodes on s_io */
> >  }
> > --- linux.orig/include/linux/writeback.h
> > +++ linux/include/linux/writeback.h
> > @@ -62,6 +62,7 @@ struct writeback_control {
> >      unsigned for_reclaim:1;        /* Invoked from the page
> > allocator
> >
>  */
> >      unsigned for_writepages:1;    /* This is a writepages() call */
> >      unsigned range_cyclic:1;    /* range_start is cyclic */
> > +    unsigned more_io:1;        /* more io to be dispatched */
> >  };
> >
> >  /*
> > --- linux.orig/mm/page-writeback.c
> > +++ linux/mm/page-writeback.c
> > @@ -558,6 +558,7 @@ static void background_writeout(unsigned
> >              global_page_state(NR_UNSTABLE_NFS) < background_thresh
> >                  && min_pages <= 0)
> >              break;
> > +        wbc.more_io = 0;
> >          wbc.encountered_congestion = 0;
> >          wbc.nr_to_write = MAX_WRITEBACK_PAGES;
> >          wbc.pages_skipped = 0;
> > @@ -565,8 +566,9 @@ static void background_writeout(unsigned
> >          min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
> >          if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
> >              /* Wrote less than expected */
> > -            congestion_wait(WRITE, HZ/10);
> > -            if (!wbc.encountered_congestion)
> > +            if (wbc.encountered_congestion || wbc.more_io)
> > +                congestion_wait(WRITE, HZ/10);
> > +            else
> >                  break;
> >          }
> >      }
> > @@ -631,11 +633,12 @@ static void wb_kupdate(unsigned long arg
> >              global_page_state(NR_UNSTABLE_NFS) +
> >              (inodes_stat.nr_inodes - inodes_stat.nr_unused);
> >      while (nr_to_write > 0) {
> > +        wbc.more_io = 0;
> >          wbc.encountered_congestion = 0;
> >          wbc.nr_to_write = MAX_WRITEBACK_PAGES;
> >          writeback_inodes(&wbc);
> >          if (wbc.nr_to_write > 0) {
> > -            if (wbc.encountered_congestion)
> > +            if (wbc.encountered_congestion || wbc.more_io)
> >                  congestion_wait(WRITE, HZ/10);
> >              else
> >                  break;    /* All the old data is written */
> >
> >
> >
>
>
>
-
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