2008-01-16 09:26:41

by Martin Knoblauch

[permalink] [raw]
Subject: Re: regression: 100% io-wait with 2.6.24-rcX

----- Original Message ----
> From: Mike Snitzer <[email protected]>
> To: Fengguang Wu <[email protected]>
> Cc: Peter Zijlstra <[email protected]>; [email protected]; Ingo Molnar <[email protected]>; [email protected]; "[email protected]" <[email protected]>; Linus Torvalds <[email protected]>; Andrew Morton <[email protected]>
> Sent: Tuesday, January 15, 2008 10:13:22 PM
> Subject: Re: regression: 100% io-wait with 2.6.24-rcX
>
> On Jan 14, 2008 7:50 AM, Fengguang Wu wrote:
> > On Mon, Jan 14, 2008 at 12:41:26PM +0100, Peter Zijlstra wrote:
> > >
> > > On Mon, 2008-01-14 at 12:30 +0100, Joerg Platte wrote:
> > > > Am Montag, 14. Januar 2008 schrieb Fengguang Wu:
> > > >
> > > > > Joerg, this patch fixed the bug for me :-)
> > > >
> > > > Fengguang, congratulations, I can confirm that your patch
> fixed
>
the bug! With
> > > > previous kernels the bug showed up after each reboot. Now,
> when
>
booting the
> > > > patched kernel everything is fine and there is no longer
> any
>
suspicious
> > > > iowait!
> > > >
> > > > Do you have an idea why this problem appeared in 2.6.24?
> Did
>
somebody change
> > > > the ext2 code or is it related to the changes in the scheduler?
> > >
> > > It was Fengguang who changed the inode writeback code, and I
> guess
>
the
> > > new and improved code was less able do deal with these funny corner
> > > cases. But he has been very good in tracking them down and
> solving
>
them,
> > > kudos to him for that work!
> >
> > Thank you.
> >
> > In particular the bug is triggered by the patch named:
> > "writeback: introduce writeback_control.more_io to
> indicate
>
more io"
> > That patch means to speed up writeback, but unfortunately its
> > aggressiveness has disclosed bugs in reiserfs, jfs and now ext2.
> >
> > Linus, given the number of bugs it triggered, I'd recommend revert
> > this patch(git commit
> 2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b).
>
Let's
> > push it back to -mm tree for more testings?
>
> Fengguang,
>
> I'd like to better understand where your writeback work stands
> relative to 2.6.24-rcX and -mm. To be clear, your changes in
> 2.6.24-rc7 have been benchmarked to provide a ~33% sequential write
> performance improvement with ext3 (as compared to 2.6.22, CFS could be
> helping, etc but...). Very impressive!
>
> Given this improvement it is unfortunate to see your request to revert
> 2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b but it is understandable if
> you're not confident in it for 2.6.24.
>
> That said, you recently posted an -mm patchset that first reverts
> 2e6883bdf49abd0e7f0d9b6297fc3be7ebb2250b and then goes on to address
> the "slow writes for concurrent large and small file writes" bug:
> http://lkml.org/lkml/2008/1/15/132
>
> 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.

Cheers
Martin






2008-01-16 12:00:05

by Wu Fengguang

[permalink] [raw]
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.

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 */

2008-01-16 12:00:04

by Wu Fengguang

[permalink] [raw]
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.

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 */