Re: regression: 100% io-wait with 2.6.24-rcX

Martin Knoblauch
2008-01-16T14:16:03Z

----- Original Message ----
> From: Fengguang Wu <wfg@mail.ustc.edu.cn>
> To: Martin Knoblauch <knobi@knobisoft.de>
> Cc: Mike Snitzer <snitzer@gmail.com>; Peter Zijlstra <peterz@infradead.org>; jplatte@naasa.net; Ingo Molnar <mingo@elte.hu>; linux-kernel@vger.kernel.org; "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>; Linus Torvalds <torvalds@linux-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.

Cheers
Martin

> 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 */
>
>
>