Fix a system hang bug introduced by commit b7a2441f ("writeback:
remove writeback_control.more_io") and e8dfc305 ("writeback: elevate
queue_io() into wb_writeback()") easily reproducible with high memory
pressure and lots of file creation/deletions, for example, a kernel
build in limited memory.

It hangs when some inode is in the I_NEW, I_FREEING or I_WILL_FREE 
state, the flusher will get stuck busy retrying that inode, never
releasing wb->list_lock. The lock in turn blocks all kinds of other
tasks when they are trying to grab it.

As put by Jan, it's a safe change regarding data integrity. I_FREEING or
I_WILL_FREE inodes are written back by iput_final() and it is reclaim
code that is responsible for eventually removing them. So writeback code
can safely ignore them. I_NEW inodes should move out of this state when
they are fully set up and in the writeback round following that, we will
consider them for writeback. So the change makes sense.                                                         

CC: Jan Kara <jack@suse.cz> 
Reported-by: NHugh Dickins <hughd@google.com>
Tested-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Originally, MAX_WRITEBACK_PAGES was hard-coded to 1024 because of a
concern of not holding I_SYNC for too long.  (At least, that was the
comment previously.)  This doesn't make sense now because the only
time we wait for I_SYNC is if we are calling sync or fsync, and in
that case we need to write out all of the data anyway.  Previously
there may have been other code paths that waited on I_SYNC, but not
any more.					    -- Theodore Ts'o

So remove the MAX_WRITEBACK_PAGES constraint. The writeback pages
will adapt to as large as the storage device can write within 500ms.

XFS is observed to do IO completions in a batch, and the batch size is
equal to the write chunk size. To avoid dirty pages to suddenly drop
out of balance_dirty_pages()'s dirty control scope and create large
fluctuations, the chunk size is also limited to half the control scope.

The balance_dirty_pages() control scrope is

	[(background_thresh + dirty_thresh) / 2, dirty_thresh]

which is by default [15%, 20%] of global dirty pages, whose range size
is dirty_thresh / DIRTY_FULL_SCOPE.

The adpative write chunk size will be rounded to the nearest 4MB
boundary.

http://bugzilla.kernel.org/show_bug.cgi?id=13930

CC: Theodore Ts'o <tytso@mit.edu>
CC: Dave Chinner <david@fromorbit.com>
CC: Chris Mason <chris.mason@oracle.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Add trace event balance_dirty_state for showing the global dirty page
counts and thresholds at each global_dirty_limits() invocation.  This
will cover the callers throttle_vm_writeout(), over_bground_thresh()
and each balance_dirty_pages() loop.
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

The max-pause limit helps to keep the sleep time inside
balance_dirty_pages() within MAX_PAUSE=200ms. The 200ms max sleep means
per task rate limit of 8pages/200ms=160KB/s when dirty exceeded, which
normally is enough to stop dirtiers from continue pushing the dirty
pages high, unless there are a sufficient large number of slow dirtiers
(eg. 500 tasks doing 160KB/s will still sum up to 80MB/s, exceeding the
write bandwidth of a slow disk and hence accumulating more and more dirty
pages).

The pass-good limit helps to let go of the good bdi's in the presence of
a blocked bdi (ie. NFS server not responding) or slow USB disk which for
some reason build up a large number of initial dirty pages that refuse
to go away anytime soon.

For example, given two bdi's A and B and the initial state

	bdi_thresh_A = dirty_thresh / 2
	bdi_thresh_B = dirty_thresh / 2
	bdi_dirty_A  = dirty_thresh / 2
	bdi_dirty_B  = dirty_thresh / 2

Then A get blocked, after a dozen seconds

	bdi_thresh_A = 0
	bdi_thresh_B = dirty_thresh
	bdi_dirty_A  = dirty_thresh / 2
	bdi_dirty_B  = dirty_thresh / 2

The (bdi_dirty_B < bdi_thresh_B) test is now useless and the dirty pages
will be effectively throttled by condition (nr_dirty < dirty_thresh).
This has two problems:
(1) we lose the protections for light dirtiers
(2) balance_dirty_pages() effectively becomes IO-less because the
    (bdi_nr_reclaimable > bdi_thresh) test won't be true. This is good
    for IO, but balance_dirty_pages() loses an important way to break
    out of the loop which leads to more spread out throttle delays.

DIRTY_PASSGOOD_AREA can eliminate the above issues. The only problem is,
DIRTY_PASSGOOD_AREA needs to be defined as 2 to fully cover the above
example while this patch uses the more conservative value 8 so as not to
surprise people with too many dirty pages than expected.

The max-pause limit won't noticeably impact the speed dirty pages are
knocked down when there is a sudden drop of global/bdi dirty thresholds.
Because the heavy dirties will be throttled below 160KB/s which is slow
enough. It does help to avoid long dirty throttle delays and especially
will make light dirtiers more responsive.
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

The start of a heavy weight application (ie. KVM) may instantly knock
down determine_dirtyable_memory() if the swap is not enabled or full.
global_dirty_limits() and bdi_dirty_limit() will in turn get global/bdi
dirty thresholds that are _much_ lower than the global/bdi dirty pages.

balance_dirty_pages() will then heavily throttle all dirtiers including
the light ones, until the dirty pages drop below the new dirty thresholds.
During this _deep_ dirty-exceeded state, the system may appear rather
unresponsive to the users.

About "deep" dirty-exceeded: task_dirty_limit() assigns 1/8 lower dirty
threshold to heavy dirtiers than light ones, and the dirty pages will
be throttled around the heavy dirtiers' dirty threshold and reasonably
below the light dirtiers' dirty threshold. In this state, only the heavy
dirtiers will be throttled and the dirty pages are carefully controlled
to not exceed the light dirtiers' dirty threshold. However if the
threshold itself suddenly drops below the number of dirty pages, the
light dirtiers will get heavily throttled.

So introduce global_dirty_limit for tracking the global dirty threshold
with policies

- follow downwards slowly
- follow up in one shot

global_dirty_limit can effectively mask out the impact of sudden drop of
dirtyable memory. It will be used in the next patch for two new type of
dirty limits. Note that the new dirty limits are not going to avoid
throttling the light dirtiers, but could limit their sleep time to 200ms.
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Introduce

	nr_dirty = NR_FILE_DIRTY + NR_WRITEBACK + NR_UNSTABLE_NFS

in order to simplify many tests in the following patches.

balance_dirty_pages() will eventually care only about the dirty sums
besides nr_writeback.
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Add a "BdiWriteBandwidth" entry and indent others in /debug/bdi/*/stats.

btw, increase digital field width to 10, for keeping the possibly
huge BdiWritten number aligned at least for desktop systems.

Impact: this could break user space tools if they are dumb enough to
depend on the number of white spaces.

CC: Theodore Ts'o <tytso@mit.edu>
CC: Jan Kara <jack@suse.cz>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

The estimation value will start from 100MB/s and adapt to the real
bandwidth in seconds.

It tries to update the bandwidth only when disk is fully utilized.
Any inactive period of more than one second will be skipped.

The estimated bandwidth will be reflecting how fast the device can
writeout when _fully utilized_, and won't drop to 0 when it goes idle.
The value will remain constant at disk idle time. At busy write time, if
not considering fluctuations, it will also remain high unless be knocked
down by possible concurrent reads that compete for the disk time and
bandwidth with async writes.

The estimation is not done purely in the flusher because there is no
guarantee for write_cache_pages() to return timely to update bandwidth.

The bdi->avg_write_bandwidth smoothing is very effective for filtering
out sudden spikes, however may be a little biased in long term.

The overheads are low because the bdi bandwidth update only occurs at
200ms intervals.

The 200ms update interval is suitable, because it's not possible to get
the real bandwidth for the instance at all, due to large fluctuations.

The NFS commits can be as large as seconds worth of data. One XFS
completion may be as large as half second worth of data if we are going
to increase the write chunk to half second worth of data. In ext4,
fluctuations with time period of around 5 seconds is observed. And there
is another pattern of irregular periods of up to 20 seconds on SSD tests.

That's why we are not only doing the estimation at 200ms intervals, but
also averaging them over a period of 3 seconds and then go further to do
another level of smoothing in avg_write_bandwidth.

CC: Li Shaohua <shaohua.li@intel.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Introduce the BDI_WRITTEN counter. It will be used for estimating the
bdi's write bandwidth.

Peter Zijlstra <a.p.zijlstra@chello.nl>:
Move BDI_WRITTEN accounting into __bdi_writeout_inc().
This will cover and fix fuse, which only calls bdi_writeout_inc().

CC: Michael Rubin <mrubin@google.com>
Reviewed-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Pass struct wb_writeback_work all the way down to writeback_sb_inodes(),
and initialize the struct writeback_control there.

struct writeback_control is basically designed to control writeback of a
single file, but we keep abuse it for writing multiple files in
writeback_sb_inodes() and its callers.

It immediately clean things up, e.g. suddenly wbc.nr_to_write vs
work->nr_pages starts to make sense, and instead of saving and restoring
pages_skipped in writeback_sb_inodes it can always start with a clean
zero value.

It also makes a neat IO pattern change: large dirty files are now
written in the full 4MB writeback chunk size, rather than whatever
remained quota in wbc->nr_to_write.
Acked-by: NJan Kara <jack@suse.cz>
Proposed-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

This helps prevent tmpfs dirtiers from skewing the per-cpu bdp_ratelimits.
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Note that it adds a little overheads to account the moved/enqueued
inodes from b_dirty to b_io. The "moved" accounting may be later used to
limit the number of inodes that can be moved in one shot, in order to
keep spinlock hold time under control.
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

It is valuable to know how the dirty inodes are iterated and their IO size.

"writeback_single_inode: bdi 8:0: ino=134246746 state=I_DIRTY_SYNC|I_SYNC age=414 index=0 to_write=1024 wrote=0"

- "state" reflects inode->i_state at the end of writeback_single_inode()
- "index" reflects mapping->writeback_index after the ->writepages() call
- "to_write" is the wbc->nr_to_write at entrance of writeback_single_inode()
- "wrote" is the number of pages actually written

v2: add trace event writeback_single_inode_requeue as proposed by Dave.

CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Remove two unused struct writeback_control fields:

	.encountered_congestion	(completely unused)
	.nonblocking		(never set, checked/showed in XFS,NFS/btrfs)

The .for_background check in nfs_write_inode() is also removed btw,
as .for_background implies WB_SYNC_NONE.
Reviewed-by: NJan Kara <jack@suse.cz>
Proposed-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

When wbc.more_io was first introduced, it indicates whether there are
at least one superblock whose s_more_io contains more IO work. Now with
the per-bdi writeback, it can be replaced with a simple b_more_io test.
Acked-by: NJan Kara <jack@suse.cz>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

This avoids unnecessary checks and dirty throttling on tmpfs/ramfs.

Notes about the tmpfs/ramfs behavior changes:

As for 2.6.36 and older kernels, the tmpfs writes will sleep inside
balance_dirty_pages() as long as we are over the (dirty+background)/2
global throttle threshold.  This is because both the dirty pages and
threshold will be 0 for tmpfs/ramfs. Hence this test will always
evaluate to TRUE:

                dirty_exceeded =
                        (bdi_nr_reclaimable + bdi_nr_writeback >= bdi_thresh)
                        || (nr_reclaimable + nr_writeback >= dirty_thresh);

For 2.6.37, someone complained that the current logic does not allow the
users to set vm.dirty_ratio=0.  So commit 4cbec4c8 changed the test to

                dirty_exceeded =
                        (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
                        || (nr_reclaimable + nr_writeback > dirty_thresh);

So 2.6.37 will behave differently for tmpfs/ramfs: it will never get
throttled unless the global dirty threshold is exceeded (which is very
unlikely to happen; once happen, will block many tasks).

I'd say that the 2.6.36 behavior is very bad for tmpfs/ramfs. It means
for a busy writing server, tmpfs write()s may get livelocked! The
"inadvertent" throttling can hardly bring help to any workload because
of its "either no throttling, or get throttled to death" property.

So based on 2.6.37, this patch won't bring more noticeable changes.

CC: Hugh Dickins <hughd@google.com>
Acked-by: NRik van Riel <riel@redhat.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NMinchan Kim <minchan.kim@gmail.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Clarify the bdi_dirty_limit() comment.
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

This removes writeback_control.wb_start and does more straightforward
sync livelock prevention by setting .older_than_this to prevent extra
inodes from being enqueued in the first place.
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Code refactor for more logical code layout.
No behavior change.

- remove the mis-named __writeback_inodes_sb()

- wb_writeback()/writeback_inodes_wb() will decide when to queue_io()
  before calling __writeback_inodes_wb()
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Split the global inode_wb_list_lock into a per-bdi_writeback list_lock,
as it's currently the most contended lock in the system for metadata
heavy workloads.  It won't help for single-filesystem workloads for
which we'll need the I/O-less balance_dirty_pages, but at least we
can dedicate a cpu to spinning on each bdi now for larger systems.

Based on earlier patches from Nick Piggin and Dave Chinner.

It reduces lock contentions to 1/4 in this test case:
10 HDD JBOD, 100 dd on each disk, XFS, 6GB ram

lock_stat version 0.3
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
vanilla 2.6.39-rc3:
                      inode_wb_list_lock:         42590          44433           0.12         147.74      144127.35         252274         886792           0.08         121.34      917211.23
                      ------------------
                      inode_wb_list_lock              2          [<ffffffff81165da5>] bdev_inode_switch_bdi+0x29/0x85
                      inode_wb_list_lock             34          [<ffffffff8115bd0b>] inode_wb_list_del+0x22/0x49
                      inode_wb_list_lock          12893          [<ffffffff8115bb53>] __mark_inode_dirty+0x170/0x1d0
                      inode_wb_list_lock          10702          [<ffffffff8115afef>] writeback_single_inode+0x16d/0x20a
                      ------------------
                      inode_wb_list_lock              2          [<ffffffff81165da5>] bdev_inode_switch_bdi+0x29/0x85
                      inode_wb_list_lock             19          [<ffffffff8115bd0b>] inode_wb_list_del+0x22/0x49
                      inode_wb_list_lock           5550          [<ffffffff8115bb53>] __mark_inode_dirty+0x170/0x1d0
                      inode_wb_list_lock           8511          [<ffffffff8115b4ad>] writeback_sb_inodes+0x10f/0x157

2.6.39-rc3 + patch:
                &(&wb->list_lock)->rlock:         11383          11657           0.14         151.69       40429.51          90825         527918           0.11         145.90      556843.37
                ------------------------
                &(&wb->list_lock)->rlock             10          [<ffffffff8115b189>] inode_wb_list_del+0x5f/0x86
                &(&wb->list_lock)->rlock           1493          [<ffffffff8115b1ed>] writeback_inodes_wb+0x3d/0x150
                &(&wb->list_lock)->rlock           3652          [<ffffffff8115a8e9>] writeback_sb_inodes+0x123/0x16f
                &(&wb->list_lock)->rlock           1412          [<ffffffff8115a38e>] writeback_single_inode+0x17f/0x223
                ------------------------
                &(&wb->list_lock)->rlock              3          [<ffffffff8110b5af>] bdi_lock_two+0x46/0x4b
                &(&wb->list_lock)->rlock              6          [<ffffffff8115b189>] inode_wb_list_del+0x5f/0x86
                &(&wb->list_lock)->rlock           2061          [<ffffffff8115af97>] __mark_inode_dirty+0x173/0x1cf
                &(&wb->list_lock)->rlock           2629          [<ffffffff8115a8e9>] writeback_sb_inodes+0x123/0x16f

hughd@google.com: fix recursive lock when bdi_lock_two() is called with new the same as old
akpm@linux-foundation.org: cleanup bdev_inode_switch_bdi() comment
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

There is no point to carry different refill policies between for_kupdate
and other type of works. Use a consistent "refill b_io iff empty" policy
which can guarantee fairness in an easy to understand way.

A b_io refill will setup a _fixed_ work set with all currently eligible
inodes and start a new round of walk through b_io. The "fixed" work set
means no new inodes will be added to the work set during the walk.
Only when a complete walk over b_io is done, new inodes that are
eligible at the time will be enqueued and the walk be started over.

This procedure provides fairness among the inodes because it guarantees
each inode to be synced once and only once at each round. So all inodes
will be free from starvations.

This change relies on wb_writeback() to keep retrying as long as we made
some progress on cleaning some pages and/or inodes. Without that ability,
the old logic on background works relies on aggressively queuing all
eligible inodes into b_io at every time. But that's not a guarantee.

The below test script completes a slightly faster now:

             2.6.39-rc3	  2.6.39-rc3-dyn-expire+
------------------------------------------------
all elapsed     256.043      252.367
stddev           24.381       12.530

tar elapsed      30.097       28.808
dd  elapsed      13.214       11.782

	#!/bin/zsh

	cp /c/linux-2.6.38.3.tar.bz2 /dev/shm/

	umount /dev/sda7
	mkfs.xfs -f /dev/sda7
	mount /dev/sda7 /fs

	echo 3 > /proc/sys/vm/drop_caches

	tic=$(cat /proc/uptime|cut -d' ' -f2)

	cd /fs
	time tar jxf /dev/shm/linux-2.6.38.3.tar.bz2 &
	time dd if=/dev/zero of=/fs/zero bs=1M count=1000 &

	wait
	sync
	tac=$(cat /proc/uptime|cut -d' ' -f2)
	echo elapsed: $((tac - tic))

It maintains roughly the same small vs. large file writeout shares, and
offers large files better chances to be written in nice 4M chunks.

Analyzes from Dave Chinner in great details:

Let's say we have lots of inodes with 100 dirty pages being created,
and one large writeback going on. We expire 8 new inodes for every
1024 pages we write back.

With the old code, we do:

	b_more_io (large inode) -> b_io (1l)
	8 newly expired inodes -> b_io (1l, 8s)

	writeback  large inode 1024 pages -> b_more_io

	b_more_io (large inode) -> b_io (8s, 1l)
	8 newly expired inodes -> b_io (8s, 1l, 8s)

	writeback  8 small inodes 800 pages
		   1 large inode 224 pages -> b_more_io

	b_more_io (large inode) -> b_io (8s, 1l)
	8 newly expired inodes -> b_io (8s, 1l, 8s)
	.....

Your new code:

	b_more_io (large inode) -> b_io (1l)
	8 newly expired inodes -> b_io (1l, 8s)

	writeback  large inode 1024 pages -> b_more_io
	(b_io == 8s)
	writeback  8 small inodes 800 pages

	b_io empty: (1800 pages written)
		b_more_io (large inode) -> b_io (1l)
		14 newly expired inodes -> b_io (1l, 14s)

	writeback  large inode 1024 pages -> b_more_io
	(b_io == 14s)
	writeback  10 small inodes 1000 pages
		   1 small inode 24 pages -> b_more_io (1l, 1s(24))
	writeback  5 small inodes 500 pages
	b_io empty: (2548 pages written)
		b_more_io (large inode) -> b_io (1l, 1s(24))
		20 newly expired inodes -> b_io (1l, 1s(24), 20s)
	......

Rough progression of pages written at b_io refill:

Old code:

	total	large file	% of writeback
	1024	224		21.9% (fixed)

New code:
	total	large file	% of writeback
	1800	1024		~55%
	2550	1024		~40%
	3050	1024		~33%
	3500	1024		~29%
	3950	1024		~26%
	4250	1024		~24%
	4500	1024		~22.7%
	4700	1024		~21.7%
	4800	1024		~21.3%
	4800	1024		~21.3%
	(pretty much steady state from here)

Ok, so the steady state is reached with a similar percentage of
writeback to the large file as the existing code. Ok, that's good,
but providing some evidence that is doesn't change the shared of
writeback to the large should be in the commit message ;)

The other advantage to this is that we always write 1024 page chunks
to the large file, rather than smaller "whatever remains" chunks.

CC: Jan Kara <jack@suse.cz>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Dynamically compute the dirty expire timestamp at queue_io() time.

writeback_control.older_than_this used to be determined at entrance to
the kupdate writeback work. This _static_ timestamp may go stale if the
kupdate work runs on and on. The flusher may then stuck with some old
busy inodes, never considering newly expired inodes thereafter.

This has two possible problems:

- It is unfair for a large dirty inode to delay (for a long time) the
  writeback of small dirty inodes.

- As time goes by, the large and busy dirty inode may contain only
  _freshly_ dirtied pages. Ignoring newly expired dirty inodes risks
  delaying the expired dirty pages to the end of LRU lists, triggering
  the evil pageout(). Nevertheless this patch merely addresses part
  of the problem.

v2: keep policy changes inside wb_writeback() and keep the
wbc.older_than_this visibility as suggested by Dave.

CC: Dave Chinner <david@fromorbit.com>
Acked-by: NJan Kara <jack@suse.cz>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NItaru Kitayama <kitayama@cl.bb4u.ne.jp>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

writeback_inodes_wb()/__writeback_inodes_sb() are not aggressive in that
they only populate possibly a subset of eligible inodes into b_io at
entrance time. When the queued set of inodes are all synced, they just
return, possibly with all queued inode pages written but still
wbc.nr_to_write > 0.

For kupdate and background writeback, there may be more eligible inodes
sitting in b_dirty when the current set of b_io inodes are completed. So
it is necessary to try another round of writeback as long as we made some
progress in this round. When there are no more eligible inodes, no more
inodes will be enqueued in queue_io(), hence nothing could/will be
synced and we may safely bail.

For example, imagine 100 inodes

        i0, i1, i2, ..., i90, i91, i99

At queue_io() time, i90-i99 happen to be expired and moved to s_io for
IO. When finished successfully, if their total size is less than
MAX_WRITEBACK_PAGES, nr_to_write will be > 0. Then wb_writeback() will
quit the background work (w/o this patch) while it's still over
background threshold. This will be a fairly normal/frequent case I guess.

Now that we do tagged sync and update inode->dirtied_when after the sync,
this change won't livelock sync(1).  I actually tried to write 1 page
per 1ms with this command

	write-and-fsync -n10000 -S 1000 -c 4096 /fs/test

and do sync(1) at the same time. The sync completes quickly on ext4,
xfs, btrfs.
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

The flusher works on dirty inodes in batches, and may quit prematurely
if the batch of inodes happen to be metadata-only dirtied: in this case
wbc->nr_to_write won't be decreased at all, which stands for "no pages
written" but also mis-interpreted as "no progress".

So introduce writeback_control.inodes_written to count the inodes get
cleaned from VFS POV.  A non-zero value means there are some progress on
writeback, in which case more writeback can be tried.
Acked-by: NJan Kara <jack@suse.cz>
Acked-by: NMel Gorman <mel@csn.ul.ie>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Explicitly update .dirtied_when on synced inodes, so that they are no
longer considered for writeback in the next round.

It can prevent both of the following livelock schemes:

- while true; do echo data >> f; done
- while true; do touch f;        done (in theory)

The exact livelock condition is, during sync(1):

(1) no new inodes are dirtied
(2) an inode being actively dirtied

On (2), the inode will be tagged and synced with .nr_to_write=LONG_MAX.
When finished, it will be redirty_tail()ed because it's still dirty
and (.nr_to_write > 0). redirty_tail() won't update its ->dirtied_when
on condition (1). The sync work will then revisit it on the next
queue_io() and find it eligible again because its old ->dirtied_when
predates the sync work start time.

We'll do more aggressive "keep writeback as long as we wrote something"
logic in wb_writeback(). The "use LONG_MAX .nr_to_write" trick in commit
b9543dac ("writeback: avoid livelocking WB_SYNC_ALL writeback") will
no longer be enough to stop sync livelock.
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
WB_SYNC_ALL sync. Identify the first stage with .tagged_writepages and
do livelock prevention for it, too.

Jan's commit f446daae ("mm: implement writeback livelock avoidance
using page tagging") is a partial fix in that it only fixed the
WB_SYNC_ALL phase livelock.

Although ext4 is tested to no longer livelock with commit f446daae,
it may due to some "redirty_tail() after pages_skipped" effect which
is by no means a guarantee for _all_ the file systems.

Note that writeback_inodes_sb() is called by not only sync(), they are
treated the same because the other callers also need livelock prevention.

Impact:  It changes the order in which pages/inodes are synced to disk.
Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
until finished with the current inode.
Acked-by: NJan Kara <jack@suse.cz>
CC: Dave Chinner <david@fromorbit.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>

Al Viro observes that in the hugetlb case, handle_mm_fault() may return
a value of the kind ENOSPC when its caller is expecting a value of the
kind VM_FAULT_SIGBUS: fix alloc_huge_page()'s failure returns.
Signed-off-by: NHugh Dickins <hughd@google.com>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6:
  ALSA: usb - turn off de-emphasis in s/pdif for cm6206
  ALSA: asihpi: Use angle brackets for system includes
  ALSA: fm801: add error handling if auto-detect fails
  ALSA: hda - Check pin support EAPD in ad198x_power_eapd_write
  ALSA: hda - Fix HP and Front pins of ad1988/ad1989 in ad198x_power_eapd()
  ALSA: 6fire: Don't leak firmware in error path
  ASoC: Fix wm_hubs input PGA ZC bits
  ASoC: Fix dapm_is_shared_kcontrol so everything isn't shared

* 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/staging:
  hwmon: (max6642): Better chip detection schema
  hwmon: (coretemp) Further relax temperature range checks
  hwmon: (coretemp) Fix TjMax detection for older CPUs
  hwmon: (coretemp) Relax target temperature range check
  hwmon: (max6642) Rename temp_fault sysfs attribute to temp2_fault

* 'for-linus' of git://android.git.kernel.org/kernel/tegra:
  ARM: Tegra: Harmony: Fix conflicting GPIO numbering

Currently, both the WM8903 and TPS6586x chips attempt to register with
gpiolib using the same GPIO numbers. This causes the audio driver to
fail to initialize.

To solve this, add a define to board-harmony.h for the TPS6586x, and make
board-harmony-power.c use this define, instead of directly referencing
TEGRA_NR_GPIOS.

This fixes a regression introduced by commit
6f168f2f.
ARM: tegra: harmony: initialize the TPS65862 PMIC
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NColin Cross <ccross@android.com>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: (25 commits)
  btrfs: fix uninitialized variable warning
  btrfs: add helper for fs_info->closing
  Btrfs: add mount -o inode_cache
  btrfs: scrub: add explicit plugging
  btrfs: use btrfs_ino to access inode number
  Btrfs: don't save the inode cache if we are deleting this root
  btrfs: false BUG_ON when degraded
  Btrfs: don't save the inode cache in non-FS roots
  Btrfs: make sure we don't overflow the free space cache crc page
  Btrfs: fix uninit variable in the delayed inode code
  btrfs: scrub: don't reuse bios and pages
  Btrfs: leave spinning on lookup and map the leaf
  Btrfs: check for duplicate entries in the free space cache
  Btrfs: don't try to allocate from a block group that doesn't have enough space
  Btrfs: don't always do readahead
  Btrfs: try not to sleep as much when doing slow caching
  Btrfs: kill BTRFS_I(inode)->block_group
  Btrfs: don't look at the extent buffer level 3 times in a row
  Btrfs: map the node block when looking for readahead targets
  Btrfs: set range_start to the right start in count_range_bits
  ...

Improve detection of MAX6642 by reading non existing registers (0x04, 0x06
and 0xff). Reading those registers returns the previously read value.
Signed-off-by: NPer Dalen <per.dalen@appeartv.com>
[guenter.roeck@ericsson.com: added second set of register reads]
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>

* git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-rc-fixes-2.6:
  [SCSI] Fix oops caused by queue refcounting failure

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6: (40 commits)
  tg3: Fix tg3_skb_error_unmap()
  net: tracepoint of net_dev_xmit sees freed skb and causes panic
  drivers/net/can/flexcan.c: add missing clk_put
  net: dm9000: Get the chip in a known good state before enabling interrupts
  drivers/net/davinci_emac.c: add missing clk_put
  af-packet: Add flag to distinguish VID 0 from no-vlan.
  caif: Fix race when conditionally taking rtnl lock
  usbnet/cdc_ncm: add missing .reset_resume hook
  vlan: fix typo in vlan_dev_hard_start_xmit()
  net/ipv4: Check for mistakenly passed in non-IPv4 address
  iwl4965: correctly validate temperature value
  bluetooth l2cap: fix locking in l2cap_global_chan_by_psm
  ath9k: fix two more bugs in tx power
  cfg80211: don't drop p2p probe responses
  Revert "net: fix section mismatches"
  drivers/net/usb/catc.c: Fix potential deadlock in catc_ctrl_run()
  sctp: stop pending timers and purge queues when peer restart asoc
  drivers/net: ks8842 Fix crash on received packet when in PIO mode.
  ip_options_compile: properly handle unaligned pointer
  iwlagn: fix incorrect PCI subsystem id for 6150 devices
  ...

With Linus' tree, today's linux-next build (powercp ppc64_defconfig)
produced this warning:

fs/btrfs/delayed-inode.c: In function 'btrfs_delayed_update_inode':
fs/btrfs/delayed-inode.c:1598:6: warning: 'ret' may be used
uninitialized in this function

Introduced by commit 16cdcec7 ("btrfs: implement delayed inode items
operation").

This fixes a bug in btrfs_update_inode(): if the returned value from
btrfs_delayed_update_inode is a nonzero garbage, inode stat data are not
updated and several call paths may hit a BUG_ON or fail with strange
code.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NDavid Sterba <dsterba@suse.cz>

wrap checking of filesystem 'closing' flag and fix a few missing memory
barriers.
Signed-off-by: NDavid Sterba <dsterba@suse.cz>

This makes the inode map cache default to off until we
fix the overflow problem when the free space crcs don't fit
inside a single page.
Signed-off-by: NChris Mason <chris.mason@oracle.com>