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

Fengguang Wu
2008-01-16T12:00:05Z

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 */