Re: [PATCH 00/11] writeback bug fixes and simplifications

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Sascha Warner]

Hi,

I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
pdflush often using 100% CPU for a long time. There seem to be some rare
pauses from its 100% usage, however.

On ~23 minutes uptime i have ~19 minutes pdflush runtime.

This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo ~x64_64

Let me know if you need more info.


Prost,
Sascha Warner

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Andrew Morton]

On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> wrote:

> Hi,
> 
> I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
> pdflush often using 100% CPU for a long time. There seem to be some rare
> pauses from its 100% usage, however.
> 
> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> 
> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo ~x64_64
> 
> Let me know if you need more info.
> 

(some) cc's restored.  Please, always do reply-to-all.

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Sascha Warner]

Andrew Morton wrote:
> On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> wrote:
>
>   
>> Hi,
>>
>> I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
>> pdflush often using 100% CPU for a long time. There seem to be some rare
>> pauses from its 100% usage, however.
>>
>> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
>>
>> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo ~x64_64
>>
>> Let me know if you need more info.
>>
>>     
>
> (some) cc's restored.  Please, always do reply-to-all.
>   
Hi Wu,

Your latest patch does fix the seen pdflush 100% issue :)

P.S.: Andrew, sorry my subject pretended I was subscribed to lkml, I am not.
I hoped for the script at lkml to pull the threads together because of
the subject.

Thank you,
Sascha Warner

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Sam Ravnborg]

> 
> P.S.: Andrew, sorry my subject pretended I was subscribed to lkml, I am not.
> I hoped for the script at lkml to pull the threads together because of
> the subject.

Find the relevant mail at lkml.org and have it forwarded to you.
Then you can do a proper reply-to-all without breaking the thread
and keeping relevant cc's.

	Sam

Re: [PATCH 00/11] writeback bug fixes and simplifications

[WU Fengguang]

On Fri, Dec 28, 2007 at 05:27:38AM +0100, Sascha Warner wrote:
> Andrew Morton wrote:
> > On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> wrote:
> >
> >   
> >> Hi,
> >>
> >> I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
> >> pdflush often using 100% CPU for a long time. There seem to be some rare
> >> pauses from its 100% usage, however.
> >>
> >> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> >>
> >> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo ~x64_64
> >>
> >> Let me know if you need more info.
> >>
> >>     
> >
> > (some) cc's restored.  Please, always do reply-to-all.
> >   
> Hi Wu,
> 
> Your latest patch does fix the seen pdflush 100% issue :)

Thank you.

Andrew: I'll be off line for some days.
The patchset will be updated some time later.

Happy new year~

Fengguang

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Hans-Peter Jansen]

Am Freitag, 28. Dezember 2007 schrieb Sascha Warner:
> Andrew Morton wrote:
> > On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> 
wrote:
> >> Hi,
> >>
> >> I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
> >> pdflush often using 100% CPU for a long time. There seem to be some
> >> rare pauses from its 100% usage, however.
> >>
> >> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> >>
> >> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo
> >> ~x64_64
> >>
> >> Let me know if you need more info.
> >
> > (some) cc's restored.  Please, always do reply-to-all.
>
> Hi Wu,

Sascha, if you want to address Fengguang by his first name, note that 
chinese and bavarians (and some others I forgot now, too) typically use the 
order:
  
  lastname firstname 

when they spell their names. Another evidence is, that the name Wu is a 
pretty common chinese family name.

Fengguang, if it's the other way around, correct me please (and I'm going to 
wear a big brown paper bag for the rest of the day..). 

> Your latest patch does fix the seen pdflush 100% issue :)
>
> P.S.: Andrew, sorry my subject pretended I was subscribed to lkml, I am
> not. I hoped for the script at lkml to pull the threads together because
> of the subject.

Such a script _cannot_ exist for a mailing list. Sane mailing list software 
mangles messages in the least intrusive way and highly depend on users 
doing the right thing. In this case, that's what Sam suggested below!

A-happy-new-year-for-all-kernel-hacking-heros-ly-yrs,

Pete

Re: [PATCH 00/11] writeback bug fixes and simplifications

[WU Fengguang]

On Sat, Dec 29, 2007 at 03:56:59PM +0100, Hans-Peter Jansen wrote:
> Am Freitag, 28. Dezember 2007 schrieb Sascha Warner:
> > Andrew Morton wrote:
> > > On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> 
> wrote:
> > >> Hi,
> > >>
> > >> I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
> > >> pdflush often using 100% CPU for a long time. There seem to be some
> > >> rare pauses from its 100% usage, however.
> > >>
> > >> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> > >>
> > >> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo
> > >> ~x64_64
> > >>
> > >> Let me know if you need more info.
> > >
> > > (some) cc's restored.  Please, always do reply-to-all.
> >
> > Hi Wu,
> 
> Sascha, if you want to address Fengguang by his first name, note that 
> chinese and bavarians (and some others I forgot now, too) typically use the 
> order:
>   
>   lastname firstname 
> 
> when they spell their names. Another evidence is, that the name Wu is a 
> pretty common chinese family name.
> 
> Fengguang, if it's the other way around, correct me please (and I'm going to 
> wear a big brown paper bag for the rest of the day..). 

You are right. We normally do "Fengguang" or "Mr. Wu" :-)
For LKML the first name is less ambiguous.

Thanks,
Fengguang

Re: [PATCH 00/11] writeback bug fixes and simplifications

[WU Fengguang]

On Fri, Dec 28, 2007 at 03:01:11PM -0800, Andrew Morton wrote:
> On Thu, 27 Dec 2007 23:08:40 +0100 Sascha Warner <prx@cinatas.ath.cx> wrote:
> 
> > Hi,
> > 
> > I applied your patches to 2.6.24-rc6-mm1, but now I am faced with one
> > pdflush often using 100% CPU for a long time. There seem to be some rare
> > pauses from its 100% usage, however.
> > 
> > On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> > 
> > This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo ~x64_64
> > 
> > Let me know if you need more info.

Sascha, Thank you for the testing.

Replace the first patch with this one should help:

---
Subject: writeback: introduce s_more_io_wait for inodes to be re-synced after a while

Introduce super_block.s_more_io_wait and writeback_control.more_io_wait.
They are for inodes that for some reason cannot be synced immediately.

These inodes will be moved to s_more_io_wait and retried after a while(waiting
up to 0.1s).  The normal lots-of-dirty-pages inodes will be moved to more_io
and be synced after other inodes in s_io have been serviced(no sleep).

The data flow is made more simple:

s_dirty --> s_io --> s_more_io/s_more_io_wait --+
             ^                                  |
	     |                                  |
	     +----------------------------------+

- to fill s_io:
		s_more_io +
		s_dirty(expired) +
		s_more_io_wait
				---> s_io
- to drain s_io:
		s_io -+--> clean inodes goto inode_in_use/inode_unused
		      |
		      +--> s_more_io
		      |
		      +--> s_more_io_wait

Obviously there's no ordering or starvation problems in the queues:
- s_dirty is now a strict FIFO queue
- inode.dirtied_when now really means the first dirty time
- once exipired, the dirty inode will stay in s_*io* queues until made clean
- the dirty inodes in s_*io* queues will be revisted in order: no starvation

Cc: Michael Rubin <mrubin@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 fs/fs-writeback.c         |   26 ++++++++++++----
 fs/super.c                |    1 
 include/linux/fs.h        |    1 
 include/linux/writeback.h |    1 
 mm/page-writeback.c       |   56 ++++++++++++++++++++----------------
 5 files changed, 55 insertions(+), 30 deletions(-)

--- linux-2.6.24-rc6-mm1.orig/fs/fs-writeback.c
+++ linux-2.6.24-rc6-mm1/fs/fs-writeback.c
@@ -172,6 +172,14 @@ static void requeue_io(struct inode *ino
 	list_move(&inode->i_list, &inode->i_sb->s_more_io);
 }
 
+/*
+ * The inode should be retried after _sleeping_ for a while.
+ */
+static void requeue_io_wait(struct inode *inode)
+{
+	list_move(&inode->i_list, &inode->i_sb->s_more_io_wait);
+}
+
 static void inode_sync_complete(struct inode *inode)
 {
 	/*
@@ -206,13 +214,15 @@ static void queue_io(struct super_block 
 {
 	list_splice_init(&sb->s_more_io, sb->s_io.prev);
 	move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
+	list_splice_init(&sb->s_more_io_wait, sb->s_io.prev);
 }
 
 int sb_has_dirty_inodes(struct super_block *sb)
 {
-	return !list_empty(&sb->s_dirty) ||
-	       !list_empty(&sb->s_io) ||
-	       !list_empty(&sb->s_more_io);
+	return !list_empty(&sb->s_dirty)   ||
+	       !list_empty(&sb->s_io)      ||
+	       !list_empty(&sb->s_more_io) ||
+	       !list_empty(&sb->s_more_io_wait);
 }
 EXPORT_SYMBOL(sb_has_dirty_inodes);
 
@@ -472,11 +482,15 @@ int generic_sync_sb_inodes(struct super_
 		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;
+		if (!list_empty(&sb->s_more_io_wait))
+			wbc->more_io_wait = 1;
 	}
-	if (!list_empty(&sb->s_more_io))
-		wbc->more_io = 1;
 	spin_unlock(&inode_lock);
 	return ret;		/* Leave any unwritten inodes on s_io */
 }
--- linux-2.6.24-rc6-mm1.orig/mm/page-writeback.c
+++ linux-2.6.24-rc6-mm1/mm/page-writeback.c
@@ -543,6 +543,34 @@ void throttle_vm_writeout(gfp_t gfp_mask
 }
 
 /*
+ * Write back up to MAX_WRITEBACK_PAGES.
+ * Return true if there's no more work.
+ */
+static int writeback_some_pages(struct writeback_control *wbc, int nr)
+{
+	int all_done = 0;
+
+	wbc->more_io = 0;
+	wbc->more_io_wait = 0;
+	wbc->encountered_congestion = 0;
+	wbc->nr_to_write = nr;
+
+	writeback_inodes(wbc);
+
+	if (wbc->encountered_congestion)
+		congestion_wait(WRITE, HZ/10);
+
+	if (wbc->more_io)
+		;
+	else if (wbc->more_io_wait)
+		congestion_wait(WRITE, HZ/10);
+	else
+		all_done = 1;
+
+	return all_done;
+}
+
+/*
  * writeback at least _min_pages, and keep writing until the amount of dirty
  * memory is less than the background threshold, or until we're all clean.
  */
@@ -553,7 +581,6 @@ static void background_writeout(unsigned
 		.bdi		= NULL,
 		.sync_mode	= WB_SYNC_NONE,
 		.older_than_this = NULL,
-		.nr_to_write	= 0,
 		.nonblocking	= 1,
 		.range_cyclic	= 1,
 	};
@@ -567,19 +594,9 @@ 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;
-		writeback_inodes(&wbc);
+		if (writeback_some_pages(&wbc, MAX_WRITEBACK_PAGES))
+			break;
 		min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
-		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
-			/* Wrote less than expected */
-			if (wbc.encountered_congestion || wbc.more_io)
-				congestion_wait(WRITE, HZ/10);
-			else
-				break;
-		}
 	}
 }
 
@@ -627,7 +644,6 @@ static void wb_kupdate(unsigned long arg
 		.bdi		= NULL,
 		.sync_mode	= WB_SYNC_NONE,
 		.older_than_this = &oldest_jif,
-		.nr_to_write	= 0,
 		.nonblocking	= 1,
 		.for_kupdate	= 1,
 		.range_cyclic	= 1,
@@ -642,16 +658,8 @@ 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 || wbc.more_io)
-				congestion_wait(WRITE, HZ/10);
-			else
-				break;	/* All the old data is written */
-		}
+		if (writeback_some_pages(&wbc, MAX_WRITEBACK_PAGES))
+			break;
 		nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 	}
 	if (time_before(next_jif, jiffies + HZ))
--- linux-2.6.24-rc6-mm1.orig/fs/super.c
+++ linux-2.6.24-rc6-mm1/fs/super.c
@@ -64,6 +64,7 @@ static struct super_block *alloc_super(s
 		INIT_LIST_HEAD(&s->s_dirty);
 		INIT_LIST_HEAD(&s->s_io);
 		INIT_LIST_HEAD(&s->s_more_io);
+		INIT_LIST_HEAD(&s->s_more_io_wait);
 		INIT_LIST_HEAD(&s->s_files);
 		INIT_LIST_HEAD(&s->s_instances);
 		INIT_HLIST_HEAD(&s->s_anon);
--- linux-2.6.24-rc6-mm1.orig/include/linux/fs.h
+++ linux-2.6.24-rc6-mm1/include/linux/fs.h
@@ -1011,6 +1011,7 @@ struct super_block {
 	struct list_head	s_dirty;	/* dirty inodes */
 	struct list_head	s_io;		/* parked for writeback */
 	struct list_head	s_more_io;	/* parked for more writeback */
+	struct list_head	s_more_io_wait;	/* parked for sleep-then-retry */
 	struct hlist_head	s_anon;		/* anonymous dentries for (nfs) exporting */
 	struct list_head	s_files;
 
--- linux-2.6.24-rc6-mm1.orig/include/linux/writeback.h
+++ linux-2.6.24-rc6-mm1/include/linux/writeback.h
@@ -63,6 +63,7 @@ struct writeback_control {
 	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 */
+	unsigned more_io_wait:1;	/* more io to be dispatched after a while */
 };
 
 /*

[PATCH 00/11] writeback bug fixes and simplifications

[Fengguang Wu]

Andrew,

Here are some writeback bug fixes and code cleanups, based on 2.6.24-rc6-mm1.

The detailed description can be found in the first patch, which introduces the
new facility for the following patches to use.

The first two patches combined should fix the "slow writes for concurrent large
and small file writes" bug which Michael Rubin tries to fix.

[PATCH 01/11] writeback: introduce s_more_io_wait for inodes to be re-synced af
[PATCH 02/11] writeback: requeue_io_wait() on blocked kupdate
[PATCH 03/11] writeback: replace redirty_tail() on more-pages-to-sync
[PATCH 04/11] writeback: requeue_io_wait() on locked inode
[PATCH 05/11] writeback: requeue_io_wait() on congested blockdev
[PATCH 06/11] writeback: requeue_io_wait() on locked buffers
[PATCH 07/11] writeback: requeue_io() on redirtied inode

More code cleanups:

[PATCH 08/11] writeback: introduce queue_dirty()
[PATCH 09/11] writeback: replace redirty_tail() on memory-backed bdi
[PATCH 10/11] writeback: remove redirty_tail()
[PATCH 11/11] writeback: __sync_single_inode() code cleanup


Diffstat:

 fs/fs-writeback.c         |  125 +++++++++++++-----------------------
 fs/super.c                |    1
 include/linux/fs.h        |    1
 include/linux/writeback.h |    1
 mm/page-writeback.c       |   56 +++++++++-------
 5 files changed, 82 insertions(+), 102 deletions(-)

Thank you,
Fengguang
--

Re: [PATCH 00/11] writeback bug fixes and simplifications

[Martin Knoblauch]

----- Original Message ----
> From: WU Fengguang <wfg@mail.ustc.edu.cn>
> To: Hans-Peter Jansen <hpj@urpla.net>
> Cc: Sascha Warner <prx@cinatas.ath.cx>; Andrew Morton <akpm@linux-foundation.org>; linux-kernel@vger.kernel.org; Peter Zijlstra <a.p.zijlstra@chello.nl>
> Sent: Wednesday, January 9, 2008 4:33:32 AM
> Subject: Re: [PATCH 00/11] writeback bug fixes and simplifications
> 
> On Sat, Dec 29, 2007 at 03:56:59PM +0100, Hans-Peter Jansen wrote:
> > Am Freitag, 28. Dezember 2007 schrieb Sascha Warner:
> > > Andrew Morton wrote:
> > > > On Thu, 27 Dec 2007 23:08:40 +0100 Sascha
> Warner
> 
  
> > wrote:
> > > >> Hi,
> > > >>
> > > >> I applied your patches to 2.6.24-rc6-mm1, but now I am
> faced
> 
 with one
> > > >> pdflush often using 100% CPU for a long time. There seem to
> be
> 
 some
> > > >> rare pauses from its 100% usage, however.
> > > >>
> > > >> On ~23 minutes uptime i have ~19 minutes pdflush runtime.
> > > >>
> > > >> This is on E6600, x86_64, 2 Gig RAM, SATA HDD, running on gentoo
> > > >> ~x64_64
> > > >>
> > > >> Let me know if you need more info.
> > > >
> > > > (some) cc's restored.  Please, always do reply-to-all.
> > >
> > > Hi Wu,
> > 
> > Sascha, if you want to address Fengguang by his first name, note
> that
> 
 
> > chinese and bavarians (and some others I forgot now, too)
> typically
> 
 use the 
> > order:
> >   
> >   lastname firstname 
> > 
> > when they spell their names. Another evidence is, that the name Wu
> is
> 
 a 
> > pretty common chinese family name.
> > 
> > Fengguang, if it's the other way around, correct me please (and
> I'm
> 
 going to 
> > wear a big brown paper bag for the rest of the day..). 
> 
> You are right. We normally do "Fengguang" or "Mr. Wu" :-)
> For LKML the first name is less ambiguous.
> 
> Thanks,
> Fengguang
> 

 Just cannot resist. Hans-Peter mentions Bavarian using Lastname-Givenname as well. This is only true in a folklore context (or when you are very deep in the countryside). Officially the bavarians use the usual German Given/Lastname. Although they will never admit to be Germans, of course :-)


Cheers
Martin