linux.git/fs/fs-writeback.c, branch v5.4-rc2

writeback: add tracepoints for cgroup foreign writebacks

2019-08-30T13:42:49+00:00

cgroup foreign inode handling has quite a bit of heuristics and
internal states which sometimes makes it difficult to understand
what's going on.  Add tracepoints to improve visibility.

Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

writeback, memcg: Implement cgroup_writeback_by_id()

2019-08-27T15:22:38+00:00

Implement cgroup_writeback_by_id() which initiates cgroup writeback
from bdi and memcg IDs.  This will be used by memcg foreign inode
flushing.

v2: Use wb_get_lookup() instead of wb_get_create() to avoid creating
    spurious wbs.

v3: Interpret 0 @nr as 1.25 * nr_dirty to implement best-effort
    flushing while avoding possible livelocks.

Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

writeback: Generalize and expose wb_completion

2019-08-27T15:22:38+00:00

wb_completion is used to track writeback completions.  We want to use
it from memcg side for foreign inode flushes.  This patch updates it
to remember the target waitq instead of assuming bdi->wb_waitq and
expose it outside of fs-writeback.c.

Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

writeback, cgroup: inode_switch_wbs() shouldn't give up on wb_switch_rwsem trylock fail

2019-08-15T19:30:46+00:00

As inode wb switching may make sync(2) miss some inodes, they're
synchronized using wb_switch_rwsem so that no wb switching happens
while sync(2) is in progress.  In addition to synchronizing the actual
switching, the rwsem is also used to prevent queueing new switch
attempts while sync(2) is in progress.  This is to avoid queueing too
many instances while the rwsem is held by sync(2).  Unfortunately,
this is too agressive and can block wb switching for a long time if
sync(2) is frequent.

The goal is avoiding expolding the number of scheduled switches, not
avoiding scheduling anything.  Let's use wb_switch_rwsem only for
synchronizing the actual switching and sync(2) and use
isw_nr_in_flight instead for limiting the maximum number of scheduled
switches.  The limit is set to 1024 which should be more than enough
while still avoiding extreme situations.

Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

writeback, cgroup: Adjust WB_FRN_TIME_CUT_DIV to accelerate foreign inode switching

2019-08-15T19:30:44+00:00

WB_FRN_TIME_CUT_DIV is used to tell the foreign inode detection logic
to ignore short writeback rounds to prevent getting confused by a
burst of short writebacks.  The parameter is currently 2 meaning that
anything smaller than half of the running average writback duration
will be ignored.

This is unnecessarily aggressive.  The detection logic uses 16 history
slots and is already reasonably protected against some short bursts
confusing it and the current parameter can lead to tens of seconds of
missed detection depending on the writeback pattern.

Let's change the parameter to 8, so that it only ignores writeback
with are smaller than 12.5% of the current running average.

v2: Add comment explaining what's going on with the foreign detection
    parameters.

Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

blkcg, writeback: Add wbc->no_cgroup_owner

2019-07-10T15:00:57+00:00

When writeback IOs are bounced through async layers, the IOs should
only be accounted against the wbc from the original bdi writeback to
avoid confusing cgroup inode ownership arbitration.  Add
wbc->no_cgroup_owner to allow disabling wbc cgroup owner accounting.
This will be used make btrfs compression work well with cgroup IO
control.

v2: Renamed from no_wbc_acct to no_cgroup_owner and added comment as
    per Jan.

Reviewed-by: Josef Bacik 
Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

blkcg, writeback: Rename wbc_account_io() to wbc_account_cgroup_owner()

2019-07-10T15:00:57+00:00

wbc_account_io() does a very specific job - try to see which cgroup is
actually dirtying an inode and transfer its ownership to the majority
dirtier if needed.  The name is too generic and confusing.  Let's
rename it to something more specific.

Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

cgroup, blkcg: Prepare some symbols for module and !CONFIG_CGROUP usages

2019-07-10T15:00:57+00:00

btrfs is going to use css_put() and wbc helpers to improve cgroup
writeback support.  Add dummy css_get() definition and export wbc
helpers to prepare for module and !CONFIG_CGROUP builds.

Reported-by: kbuild test robot 
Reviewed-by: Jan Kara 
Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

blkcg, writeback: dead memcgs shouldn't contribute to writeback ownership arbitration

2019-06-15T16:39:42+00:00

wbc_account_io() collects information on cgroup ownership of writeback
pages to determine which cgroup should own the inode.  Pages can stay
associated with dead memcgs but we want to avoid attributing IOs to
dead blkcgs as much as possible as the association is likely to be
stale.  However, currently, pages associated with dead memcgs
contribute to the accounting delaying and/or confusing the
arbitration.

Fix it by ignoring pages associated with dead memcgs.

Signed-off-by: Tejun Heo 
Cc: Jan Kara 
Signed-off-by: Jens Axboe

treewide: Add SPDX license identifier for missed files

2019-05-21T08:50:45+00:00

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have EXPORT_.*_SYMBOL_GPL inside which was used in the
   initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman