Commit Graph

70 Commits

Author SHA1 Message Date
Gustavo F. Padovan 345227d705 backing-dev: Kill set but not used var in bdi_debug_stats_show()
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-05-20 21:23:37 +02:00
Lucas De Marchi 25985edced Fix common misspellings
Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
2011-03-31 11:26:23 -03:00
Linus Torvalds d39dd11c3e Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
  fs: simplify iget & friends
  fs: pull inode->i_lock up out of writeback_single_inode
  fs: rename inode_lock to inode_hash_lock
  fs: move i_wb_list out from under inode_lock
  fs: move i_sb_list out from under inode_lock
  fs: remove inode_lock from iput_final and prune_icache
  fs: Lock the inode LRU list separately
  fs: factor inode disposal
  fs: protect inode->i_state with inode->i_lock
  autofs4: Do not potentially dereference NULL pointer returned by fget() in autofs_dev_ioctl_setpipefd()
  autofs4 - remove autofs4_lock
  autofs4 - fix d_manage() return on rcu-walk
  autofs4 - fix autofs4_expire_indirect() traversal
  autofs4 - fix dentry leak in autofs4_expire_direct()
  autofs4 - reinstate last used update on access
  vfs - check non-mountpoint dentry might block in __follow_mount_rcu()
2011-03-24 19:01:30 -07:00
Dave Chinner a66979abad fs: move i_wb_list out from under inode_lock
Protect the inode writeback list with a new global lock
inode_wb_list_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-24 21:17:51 -04:00
Jens Axboe 95f28604a6 fs: assign sb->s_bdi to default_backing_dev_info if the bdi is going away
We don't have proper reference counting for this yet, so we run into
cases where the device is pulled and we OOPS on flushing the fs data.
This happens even though the dirty inodes have already been
migrated to the default_backing_dev_info.

Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Tested-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-03-17 11:13:12 +01:00
Jens Axboe 7eaceaccab block: remove per-queue plugging
Code has been converted over to the new explicit on-stack plugging,
and delay users have been converted to use the new API for that.
So lets kill off the old plugging along with aops->sync_page().

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-03-10 08:52:07 +01:00
Linus Torvalds 426e1f5cec Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: (52 commits)
  split invalidate_inodes()
  fs: skip I_FREEING inodes in writeback_sb_inodes
  fs: fold invalidate_list into invalidate_inodes
  fs: do not drop inode_lock in dispose_list
  fs: inode split IO and LRU lists
  fs: switch bdev inode bdi's correctly
  fs: fix buffer invalidation in invalidate_list
  fsnotify: use dget_parent
  smbfs: use dget_parent
  exportfs: use dget_parent
  fs: use RCU read side protection in d_validate
  fs: clean up dentry lru modification
  fs: split __shrink_dcache_sb
  fs: improve DCACHE_REFERENCED usage
  fs: use percpu counter for nr_dentry and nr_dentry_unused
  fs: simplify __d_free
  fs: take dcache_lock inside __d_path
  fs: do not assign default i_ino in new_inode
  fs: introduce a per-cpu last_ino allocator
  new helper: ihold()
  ...
2010-10-26 17:58:44 -07:00
Peter Zijlstra 766f916419 kernel: remove PF_FLUSHER
PF_FLUSHER is only ever set, not tested, remove it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-26 16:52:15 -07:00
Mel Gorman 0e093d9976 writeback: do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone
If congestion_wait() is called with no BDI congested, the caller will
sleep for the full timeout and this may be an unnecessary sleep.  This
patch adds a wait_iff_congested() that checks congestion and only sleeps
if a BDI is congested else, it calls cond_resched() to ensure the caller
is not hogging the CPU longer than its quota but otherwise will not sleep.

This is aimed at reducing some of the major desktop stalls reported during
IO.  For example, while kswapd is operating, it calls congestion_wait()
but it could just have been reclaiming clean page cache pages with no
congestion.  Without this patch, it would sleep for a full timeout but
after this patch, it'll just call schedule() if it has been on the CPU too
long.  Similar logic applies to direct reclaimers that are not making
enough progress.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-26 16:52:07 -07:00
Mel Gorman 52bb919866 writeback: account for time spent congestion_waited
There is strong evidence to indicate a lot of time is being spent in
congestion_wait(), some of it unnecessarily.  This patch adds a tracepoint
for congestion_wait to record when congestion_wait() was called, how long
the timeout was for and how long it actually slept.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-26 16:52:07 -07:00
Nick Piggin 7ccf19a804 fs: inode split IO and LRU lists
The use of the same inode list structure (inode->i_list) for two
different list constructs with different lifecycles and purposes
makes it impossible to separate the locking of the different
operations. Therefore, to enable the separation of the locking of
the writeback and reclaim lists, split the inode->i_list into two
separate lists dedicated to their specific tracking functions.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2010-10-25 21:26:15 -04:00
Jan Kara 976e48f8a5 bdi: Initialize noop_backing_dev_info properly
Properly initialize this backing dev info so that writeback code does not
barf when getting to it e.g. via sb->s_bdi.

Cc: stable@kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-09-22 09:48:47 +02:00
Artem Bityutskiy 6628bc74f1 writeback: do not lose wakeup events when forking bdi threads
This patch fixes the following issue:

INFO: task mount.nfs4:1120 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
mount.nfs4    D 00000000fffc6a21     0  1120   1119 0x00000000
 ffff880235643948 0000000000000046 ffffffff00000000 ffffffff00000000
 ffff880235643fd8 ffff880235314760 00000000001d44c0 ffff880235643fd8
 00000000001d44c0 00000000001d44c0 00000000001d44c0 00000000001d44c0
Call Trace:
 [<ffffffff813bc747>] schedule_timeout+0x34/0xf1
 [<ffffffff813bc530>] ? wait_for_common+0x3f/0x130
 [<ffffffff8106b50b>] ? trace_hardirqs_on+0xd/0xf
 [<ffffffff813bc5c3>] wait_for_common+0xd2/0x130
 [<ffffffff8104159c>] ? default_wake_function+0x0/0xf
 [<ffffffff813beaa0>] ? _raw_spin_unlock+0x26/0x2a
 [<ffffffff813bc6bb>] wait_for_completion+0x18/0x1a
 [<ffffffff81101a03>] sync_inodes_sb+0xca/0x1bc
 [<ffffffff811056a6>] __sync_filesystem+0x47/0x7e
 [<ffffffff81105798>] sync_filesystem+0x47/0x4b
 [<ffffffff810e7ffd>] generic_shutdown_super+0x22/0xd2
 [<ffffffff810e80f8>] kill_anon_super+0x11/0x4f
 [<ffffffffa00d06d7>] nfs4_kill_super+0x3f/0x72 [nfs]
 [<ffffffff810e7b68>] deactivate_locked_super+0x21/0x41
 [<ffffffff810e7fd6>] deactivate_super+0x40/0x45
 [<ffffffff810fc66c>] mntput_no_expire+0xb8/0xed
 [<ffffffff810fc73b>] release_mounts+0x9a/0xb0
 [<ffffffff810fc7bb>] put_mnt_ns+0x6a/0x7b
 [<ffffffffa00d0fb2>] nfs_follow_remote_path+0x19a/0x296 [nfs]
 [<ffffffffa00d11ca>] nfs4_try_mount+0x75/0xaf [nfs]
 [<ffffffffa00d1790>] nfs4_get_sb+0x276/0x2ff [nfs]
 [<ffffffff810e7dba>] vfs_kern_mount+0xb8/0x196
 [<ffffffff810e7ef6>] do_kern_mount+0x48/0xe8
 [<ffffffff810fdf68>] do_mount+0x771/0x7e8
 [<ffffffff810fe062>] sys_mount+0x83/0xbd
 [<ffffffff810089c2>] system_call_fastpath+0x16/0x1b

The reason of this hang was a race condition: when the flusher thread is
forking a bdi thread, we use 'kthread_run()', so we run it _before_ we make it
visible in 'bdi->wb.task'. The bdi thread runs, does all works, and goes sleep.
'bdi->wb.task' is still NULL. And this is a dangerous time window.

If at this time someone queues a work for this bdi, he does not see the bdi
thread and wakes up the forker thread instead! But the forker has already
forked this bdi thread, but just did not make it visible yet!

The result is that we lose the wake up event for this bdi thread and the NFS4
code waits forever.

To fix the problem, we should use 'ktrhead_create()' for creating bdi threads,
then make them visible in 'bdi->wb.task', and only after this wake them up.
This is exactly what this patch does.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-27 09:16:18 +02:00
Wu Fengguang 16c4042f08 writeback: avoid unnecessary calculation of bdi dirty thresholds
Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), so
that the latter can be avoided when under global dirty background
threshold (which is the normal state for most systems).

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-08-12 08:43:29 -07:00
Jens Axboe 6bf05d03ea writeback: fix bad _bh spinlock nesting
Fix a bug where a lock is _bh nested within another _bh lock,
but forgets to use the _bh variant for unlock.

Further more, it's not necessary to test _bh locks, the inner lock
can just use spin_lock(). So fix up the bug by making that change.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:57 +02:00
Artem Bityutskiy c284de61db writeback: cleanup bdi_register
This patch makes sure we first initialize everything and set the BDI_registered
flag, and only after this we add the bdi to 'bdi_list'. Current code adds the
bdi to the list too early, and as a result I the

WARN(!test_bit(BDI_registered, &bdi->state)

in bdi forker is triggered. Also, it is in general good practice to make things
visible only when they are fully initialized.

Also, this patch does few micro clean-ups:
1. Removes the 'exit' label which does not do anything, just returns. This
   allows to get rid of few braces and 'ret' variable and make the code smaller.
2. If 'kthread_run()' fails, remove the error code it returns, not hard-coded
   '-ENOMEM'. Theoretically, some day 'kthread_run()' can return something
   else. Also, in case of failure it is not necessary to set 'bdi->wb.task' to
   NULL.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:57 +02:00
Artem Bityutskiy 603320239f writeback: add new tracepoints
Add 2 new trace points to the periodic write-back wake up case, just like we do
in the 'bdi_queue_work()' function. Namely, introduce:

1. trace_writeback_wake_thread(bdi)
2. trace_writeback_wake_forker_thread(bdi)

The first event is triggered every time we wake up a bdi thread to start
periodic background write-out. The second event is triggered only when the bdi
thread does not exist and should be created by the forker thread.

This patch was suggested by Dave Chinner and Christoph Hellwig.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy b5048a6cb5 writeback: remove unnecessary init_timer call
The 'setup_timer()' function also calls 'init_timer()', so the extra
'init_timer()' call is not needed. Indeed, 'setup_timer()' is basically
'init_timer()' plus callback function and data pointers initialization.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy 6467716a37 writeback: optimize periodic bdi thread wakeups
Whe the first inode for a bdi is marked dirty, we wake up the bdi thread which
should take care of the periodic background write-out. However, the write-out
will actually start only 'dirty_writeback_interval' centisecs later, so we can
delay the wake-up.

This change was requested by Nick Piggin who pointed out that if we delay the
wake-up, we weed out 2 unnecessary contex switches, which matters because
'__mark_inode_dirty()' is a hot-path function.

This patch introduces a new function - 'bdi_wakeup_thread_delayed()', which
sets up a timer to wake-up the bdi thread and returns. So the wake-up is
delayed.

We also delete the timer in bdi threads just before writing-back. And
synchronously delete it when unregistering bdi. At the unregister point the bdi
does not have any users, so no one can arm it again.

Since now we take 'bdi->wb_lock' in the timer, which can execute in softirq
context, we have to use 'spin_lock_bh()' for 'bdi->wb_lock'. This patch makes
this change as well.

This patch also moves the 'bdi_wb_init()' function down in the file to avoid
forward-declaration of 'bdi_wakeup_thread_delayed()'.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy 253c34e9b1 writeback: prevent unnecessary bdi threads wakeups
Finally, we can get rid of unnecessary wake-ups in bdi threads, which are very
bad for battery-driven devices.

There are two types of activities bdi threads do:
1. process bdi works from the 'bdi->work_list'
2. periodic write-back

So there are 2 sources of wake-up events for bdi threads:

1. 'bdi_queue_work()' - submits bdi works
2. '__mark_inode_dirty()' - adds dirty I/O to bdi's

The former already has bdi wake-up code. The latter does not, and this patch
adds it.

'__mark_inode_dirty()' is hot-path function, but this patch adds another
'spin_lock(&bdi->wb_lock)' there. However, it is taken only in rare cases when
the bdi has no dirty inodes. So adding this spinlock should be fine and should
not affect performance.

This patch makes sure bdi threads and the forker thread do not wake-up if there
is nothing to do. The forker thread will nevertheless wake up at least every
5 min. to check whether it has to kill a bdi thread. This can also be optimized,
but is not worth it.

This patch also tidies up the warning about unregistered bid, and turns it from
an ugly crocodile to a simple 'WARN()' statement.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy fff5b85aa4 writeback: move bdi threads exiting logic to the forker thread
Currently, bdi threads can decide to exit if there were no useful activities
for 5 minutes. However, this causes nasty races: we can easily oops in the
'bdi_queue_work()' if the bdi thread decides to exit while we are waking it up.

And even if we do not oops, but the bdi tread exits immediately after we wake
it up, we'd lose the wake-up event and have an unnecessary delay (up to 5 secs)
in the bdi work processing.

This patch makes the forker thread to be the central place which not only
creates bdi threads, but also kills them if they were inactive long enough.
This better design-wise.

Another reason why this change was done is to prepare for the further changes
which will prevent the bdi threads from waking up every 5 sec and wasting
power. Indeed, when the task does not wake up periodically anymore, it won't be
able to exit either.

This patch also moves the the 'wake_up_bit()' call from the bdi thread to the
forker thread as well. So now the forker thread sets the BDI_pending bit, then
forks the task or kills it, then clears the bit and wakes up the waiting
process.

The only process which may wain on the bit is 'bdi_wb_shutdown()'. This
function was changed as well - now it first removes the bdi from the
'bdi_list', then waits on the 'BDI_pending' bit. Once it wakes up, it is
guaranteed that the forker thread won't race with it, because the bdi is not
visible. Note, the forker thread sets the 'BDI_pending' bit under the
'bdi->wb_lock' which is essential for proper serialization.

And additionally, when we change 'bdi->wb.task', we now take the
'bdi->work_lock', to make sure that we do not lose wake-ups which we otherwise
would when raced with, say, 'bdi_queue_work()'.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy adf3924070 writeback: restructure bdi forker loop a little
This patch re-structures the bdi forker a little:
1. Add 'bdi_cap_flush_forker(bdi)' condition check to the bdi loop. The reason
   for this is that the forker thread can start _before_ the 'BDI_registered'
   flag is set (see 'bdi_register()'), so the WARN() statement will fire for
   the default bdi. I observed this warning at boot-up.

2. Introduce an enum 'action' and use "switch" statement in the outer loop.
   This is a preparation to the further patch which will teach the forker
   thread killing bdi threads, so we'll have another case in the "switch"
   statement. This change was suggested by Christoph Hellwig.

This patch is just a small step towards the coming change where the forker
thread will kill the bdi threads. It should simplify reviewing the following
changes, which would otherwise be larger.

This patch also amends comments a little.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy 78c40cb658 writeback: do not remove bdi from bdi_list
The forker thread removes bdis from 'bdi_list' before forking the bdi thread.
But this is wrong for at least 2 reasons.

Reason #1: if we temporary remove a bdi from the list, we may miss works which
           would otherwise be given to us.

Reason #2: this is racy; indeed, 'bdi_wb_shutdown()' expects that bdis are
           always in the 'bdi_list' (see 'bdi_remove_from_list()'), and when
           it races with the forker thread, it can shut down the bdi thread
           at the same time as the forker creates it.

This patch makes sure the forker thread never removes bdis from 'bdi_list'
(which was suggested by Christoph Hellwig).

In order to make sure that we do not race with 'bdi_wb_shutdown()', we have to
hold the 'bdi_lock' while walking the 'bdi_list' and setting the 'BDI_pending'
flag.

NOTE! The error path is interesting. Currently, when we fail to create a bdi
thread, we move the bdi to the tail of 'bdi_list'. But if we never remove the
bdi from the list, we cannot move it to the tail either, because then we can
mess up the RCU readers which walk the list. And also, we'll have the race
described above in "Reason #2".

But I not think that adding to the tail is any important so I just do not do
that.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy 080dcec417 writeback: simplify bdi code a little
This patch simplifies bdi code a little by removing the 'pending_list' which is
redundant. Indeed, currently the forker thread ('bdi_forker_thread()') is
working like this:

1. In a loop, fetch all bdi's which have works but have no writeback thread and
   move them to the 'pending_list'.
2. If the list is empty, sleep for 5 sec.
3. Otherwise, take one bdi from the list, fork the writeback thread for this
   bdi, and repeat the loop.

IOW, it first moves everything to the 'pending_list', then process only one
element, and so on. This patch simplifies the algorithm, which is now as
follows.

1. Find the first bdi which has a work and remove it from the global list of
   bdi's (bdi_list).
2. If there was not such bdi, sleep 5 sec.
3. Fork the writeback thread for this bdi and repeat the loop.

IOW, now we find the first bdi to process, process it, and so on. This is
simpler and involves less lists.

The bonus now is that we can get rid of a couple of functions, as well as
remove complications which involve 'rcu_call()' and 'bdi->rcu_head'.

This patch also makes sure we use 'list_add_tail_rcu()', instead of plain
'list_add_tail()', but this piece of code is going to be removed in the next
patch anyway.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:56 +02:00
Artem Bityutskiy c4ec7908c2 writeback: do not lose wake-ups in the forker thread - 2
Currently, if someone submits jobs for the default bdi, we can lose wake-up
events. E.g., this can happen if 'bdi_queue_work()' is called when
'bdi_forker_thread()' is executing code after 'wb_do_writeback(me, 0)', but
before 'set_current_state(TASK_INTERRUPTIBLE)'.

This situation is unlikely, and the result is not very severe - we'll just
delay the execution of the work, but this is still not very nice.

This patch fixes the issue by checking whether the default bdi has works before
the forker thread goes sleep.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:55 +02:00
Artem Bityutskiy c5f7ad233b writeback: do not lose wake-ups in the forker thread - 1
Currently the forker thread can lose wake-ups which may lead to unnecessary
delays in processing bdi works. E.g., consider the following scenario.

1. 'bdi_forker_thread()' walks the 'bdi_list', finds out there is nothing to
   do, and is about to finish the loop.
2. A bdi thread decides to exit because it was inactive for long time.
3. 'bdi_queue_work()' adds a work to the bdi which just exited, so it wakes up
   the forker thread.
4. but 'bdi_forker_thread()' executes 'set_current_state(TASK_INTERRUPTIBLE)'
   and goes sleep. We lose a wake-up.

Losing the wake-up is not fatal, but this means that the bdi work processing
will be delayed by up to 5 sec. This race is theoretical, I never hit it, but
it is worth fixing.

The fix is to execute 'set_current_state(TASK_INTERRUPTIBLE)' _before_ walking
'bdi_list', not after.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:55 +02:00
Artem Bityutskiy 94eac5e623 writeback: fix possible race when creating bdi threads
This patch fixes a very unlikely race condition on the bdi forker thread error
path: when bdi thread creation fails, 'bdi->wb.task' may contain the error code
for a short period of time. If at the same time someone submits a work to this
bdi, we can end up with an oops 'bdi_queue_work()' while executing
'wake_up_process(wb->task)'.

This patch fixes the issue by introducing a temporary variable 'task' and
storing the possible error code there, so that 'wb->task' would never take
erroneous values.

Note, this race is very unlikely and I never hit it, so it is theoretical, but
nevertheless worth fixing.

This patch also merges 2 comments which were previously separate.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:19 +02:00
Artem Bityutskiy 6f904ff0e3 writeback: harmonize writeback threads naming
The write-back code mixes words "thread" and "task" for the same things. This
is not a big deal, but still an inconsistency.

hch: a convention I tend to use and I've seen in various places
is to always use _task for the storage of the task_struct pointer,
and thread everywhere else.  This especially helps with having
foo_thread for the actual thread and foo_task for a global
variable keeping the task_struct pointer

This patch renames:
* 'bdi_add_default_flusher_task()' -> 'bdi_add_default_flusher_thread()'
* 'bdi_forker_task()'              -> 'bdi_forker_thread()'

because bdi threads are 'bdi_writeback_thread()', so these names are more
consistent.

This patch also amends commentaries and makes them refer the forker and bdi
threads as "thread", not "task".

Also, while on it, make 'bdi_add_default_flusher_thread()' declaration use
'static void' instead of 'void static' and make checkpatch.pl happy.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:53:16 +02:00
Dave Chinner 455b286468 writeback: Initial tracing support
Trace queue/sched/exec parts of the writeback loop. This provides
insight into when and why flusher threads are scheduled to run. e.g
a sync invocation leaves traces like:

     sync-[...]: writeback_queue: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0
flush-8:0-[...]: writeback_exec: bdi 8:0: sb_dev 8:1 nr_pages=7712 sync_mode=0 kupdate=0 range_cyclic=0 background=0

This also lays the foundation for adding more writeback tracing to
provide deeper insight into the whole writeback path.

The original tracing code is from Jens Axboe, though this version is
a rewrite as a result of the code being traced changing
significantly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:24:23 +02:00
Christoph Hellwig 082439004b writeback: merge bdi_writeback_task and bdi_start_fn
Move all code for the writeback thread into fs/fs-writeback.c instead of
splitting it over two functions in two files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:23:06 +02:00
Christoph Hellwig c1955ce32f writeback: remove wb_list
The wb_list member of struct backing_device_info always has exactly one
element.  Just use the direct bdi->wb pointer instead and simplify some
code.

Also remove bdi_task_init which is now trivial to prepare for the next
patch.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-08-07 18:23:03 +02:00
Christoph Hellwig 83ba7b071f writeback: simplify the write back thread queue
First remove items from work_list as soon as we start working on them.  This
means we don't have to track any pending or visited state and can get
rid of all the RCU magic freeing the work items - we can simply free
them once the operation has finished.  Second use a real completion for
tracking synchronous requests - if the caller sets the completion pointer
we complete it, otherwise use it as a boolean indicator that we can free
the work item directly.  Third unify struct wb_writeback_args and struct
bdi_work into a single data structure, wb_writeback_work.  Previous we
set all parameters into a struct wb_writeback_args, copied it into
struct bdi_work, copied it again on the stack to use it there.  Instead
of just allocate one structure dynamically or on the stack and use it
all the way through the stack.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-07-06 08:59:53 +02:00
Christoph Hellwig 9c3a8ee8a1 writeback: remove writeback_inodes_wbc
This was just an odd wrapper around writeback_inodes_wb.  Removing this
also allows to get rid of the bdi member of struct writeback_control
which was rather out of place there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2010-07-06 08:54:03 +02:00
Jens Axboe 6423104b6a writeback: fixups for !dirty_writeback_centisecs
Commit 69b62d01 fixed up most of the places where we would enter
busy schedule() spins when disabling the periodic background
writeback. This fixes up the sb timer so that it doesn't get
hammered on with the delay disabled, and ensures that it gets
rearmed if needed when /proc/sys/vm/dirty_writeback_centisecs
gets modified.

bdi_forker_task() also needs to check for !dirty_writeback_centisecs
and use schedule() appropriately, fix that up too.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2010-05-21 20:00:35 +02:00
Jörn Engel 5129a469a9 Catch filesystems lacking s_bdi
noop_backing_dev_info is used only as a flag to mark filesystems that
don't have any backing store, like tmpfs, procfs, spufs, etc.

Signed-off-by: Joern Engel <joern@logfs.org>

Changed the BUG_ON() to a WARN_ON(). Note that adding dirty inodes
to the noop_backing_dev_info is not legal and will not result in
them being flushed, but we already catch this condition in
__mark_inode_dirty() when checking for a registered bdi.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2010-04-25 08:54:42 +02:00
Jens Axboe c3c532061e bdi: add helper function for doing init and register of a bdi for a file system
Pretty trivial helper, just sets up the bdi and registers it. An atomic
sequence count is used to ensure that the registered sysfs names are
unique.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2010-04-22 11:39:36 +02:00
Anton Blanchard 1442145373 backing-dev: Handle class_create() failure
I hit this when we had a bug in IDR for a few days. Basically sysfs would
fail to create new inodes since it uses an IDR and therefore class_create would
fail.

While we are unlikely to see this fail we may as well handle it instead of
oopsing.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2010-04-02 09:46:55 +02:00
OGAWA Hirofumi bf7ec5bb61 flusher: Fix PF_FROZEN race
To touch task->flags directly is racy. thaw_process() still has race
(changing non_current->flags, but this is another issue) though, I think
it's much better off.

So, use thaw_process() instead.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-12-03 13:49:43 +01:00
Romit Dasgupta c62b17a58a Thaw refrigerated bdi flusher threads before invoking kthread_stop on them
Unfreezes the bdi flusher task when the said task needs to exit.

Steps to reproduce this.
1) Mount a file system from MMC/SD card.
2) Unmount the file system. This creates a flusher task.
3) Attempt suspend to RAM. System is unresponsive.

This is because the bdi flusher thread is already in the refrigerator and will
remain so until it is thawed. The MMC driver suspend routine call stack will
ultimately issue a 'kthread_stop' on the bdi flusher thread and will block
until the flusher thread is exited. Since the bdi flusher thread is in the
refrigerator it never cleans up until thawed.

Signed-off-by: Romit Dasgupta <romit@ti.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-11-12 13:08:11 +01:00
Jens Axboe 8c4db3355b backing-dev: bdi sb prune should be in the unregister path, not destroy
Commit 592b09a42f was different from
the tested path, in that it moved the bdi super_block prune from
unregister to destroy context. This doesn't fully fix the sync hang
bug on unexpected device removal, as need to prune the bdi cache
pointer before killing flusher thread.

Tested-by: Artur Skawina <art.08.09@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-11-03 20:18:44 +01:00
Jens Axboe 592b09a42f backing-dev: ensure that a removed bdi no longer has super_block referencing it
When the bdi is being removed, we have to ensure that no super_blocks
currently have that cached in sb->s_bdi. Normally this is ensured by
the sb having a longer life span than the bdi, but if the device is
suddenly yanked, we have to kill this reference. sb->s_bdi is pointed
to freed memory at that point.

This fixes a problem with sync(1) hanging when a USB stick is pulled
without cleanly umounting it first.

Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-10-29 11:46:12 +01:00
Wu Fengguang 961515f613 writeback: kill space in debugfs item name
The space is not script friendly, kill it.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-10-09 13:01:27 +02:00
Jens Axboe ce5f8e7795 writeback: splice dirty inode entries to default bdi on bdi_destroy()
We cannot safely ensure that the inodes are all gone at this point
in time, and we must not destroy this bdi with inodes having off it.
So just splice our entries to the default bdi since that one will
always persist.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-16 15:18:52 +02:00
Jens Axboe cfc4ba5365 writeback: use RCU to protect bdi_list
Now that bdi_writeback_all() no longer handles integrity writeback,
it doesn't have to block anymore. This means that we can switch
bdi_list reader side protection to RCU.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-16 15:18:51 +02:00
Jens Axboe 500b067c5e writeback: check for registered bdi in flusher add and inode dirty
Also a debugging aid. We want to catch dirty inodes being added to
backing devices that don't do writeback.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-11 09:20:26 +02:00
Jens Axboe d993831fa7 writeback: add name to backing_dev_info
This enables us to track who does what and print info. Its main use
is catching dirty inodes on the default_backing_dev_info, so we can
fix that up.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-11 09:20:26 +02:00
Jens Axboe f09b00d3e7 writeback: add some debug inode list counters to bdi stats
Add some debug entries to be able to inspect the internal state of
the writeback details.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-11 09:20:26 +02:00
Jens Axboe 03ba3782e8 writeback: switch to per-bdi threads for flushing data
This gets rid of pdflush for bdi writeout and kupdated style cleaning.
pdflush writeout suffers from lack of locality and also requires more
threads to handle the same workload, since it has to work in a
non-blocking fashion against each queue. This also introduces lumpy
behaviour and potential request starvation, since pdflush can be starved
for queue access if others are accessing it. A sample ffsb workload that
does random writes to files is about 8% faster here on a simple SATA drive
during the benchmark phase. File layout also seems a LOT more smooth in
vmstat:

 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 0  1      0 608848   2652 375372    0    0     0 71024  604    24  1 10 48 42
 0  1      0 549644   2712 433736    0    0     0 60692  505    27  1  8 48 44
 1  0      0 476928   2784 505192    0    0     4 29540  553    24  0  9 53 37
 0  1      0 457972   2808 524008    0    0     0 54876  331    16  0  4 38 58
 0  1      0 366128   2928 614284    0    0     4 92168  710    58  0 13 53 34
 0  1      0 295092   3000 684140    0    0     0 62924  572    23  0  9 53 37
 0  1      0 236592   3064 741704    0    0     4 58256  523    17  0  8 48 44
 0  1      0 165608   3132 811464    0    0     0 57460  560    21  0  8 54 38
 0  1      0 102952   3200 873164    0    0     4 74748  540    29  1 10 48 41
 0  1      0  48604   3252 926472    0    0     0 53248  469    29  0  7 47 45

where vanilla tends to fluctuate a lot in the creation phase:

 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  1      0 678716   5792 303380    0    0     0 74064  565    50  1 11 52 36
 1  0      0 662488   5864 319396    0    0     4   352  302   329  0  2 47 51
 0  1      0 599312   5924 381468    0    0     0 78164  516    55  0  9 51 40
 0  1      0 519952   6008 459516    0    0     4 78156  622    56  1 11 52 37
 1  1      0 436640   6092 541632    0    0     0 82244  622    54  0 11 48 41
 0  1      0 436640   6092 541660    0    0     0     8  152    39  0  0 51 49
 0  1      0 332224   6200 644252    0    0     4 102800  728    46  1 13 49 36
 1  0      0 274492   6260 701056    0    0     4 12328  459    49  0  7 50 43
 0  1      0 211220   6324 763356    0    0     0 106940  515    37  1 10 51 39
 1  0      0 160412   6376 813468    0    0     0  8224  415    43  0  6 49 45
 1  1      0  85980   6452 886556    0    0     4 113516  575    39  1 11 54 34
 0  2      0  85968   6452 886620    0    0     0  1640  158   211  0  0 46 54

A 10 disk test with btrfs performs 26% faster with per-bdi flushing. A
SSD based writeback test on XFS performs over 20% better as well, with
the throughput being very stable around 1GB/sec, where pdflush only
manages 750MB/sec and fluctuates wildly while doing so. Random buffered
writes to many files behave a lot better as well, as does random mmap'ed
writes.

A separate thread is added to sync the super blocks. In the long term,
adding sync_supers_bdi() functionality could get rid of this thread again.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-11 09:20:25 +02:00
Jens Axboe 66f3b8e2e1 writeback: move dirty inodes from super_block to backing_dev_info
This is a first step at introducing per-bdi flusher threads. We should
have no change in behaviour, although sb_has_dirty_inodes() is now
ridiculously expensive, as there's no easy way to answer that question.
Not a huge problem, since it'll be deleted in subsequent patches.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-09-11 09:20:25 +02:00
Jens Axboe 8aa7e847d8 Fix congestion_wait() sync/async vs read/write confusion
Commit 1faa16d228 accidentally broke
the bdi congestion wait queue logic, causing us to wait on congestion
for WRITE (== 1) when we really wanted BLK_RW_ASYNC (== 0) instead.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2009-07-10 20:31:53 +02:00