[PATCHSET v3 btrfs/for-next] btrfs: fix cgroup writeback support

[Tejun Heo <tj@kernel.org>]

Hello,

This patchset contains only the btrfs part of the following patchset.

  [1] [PATCHSET v2 btrfs/for-next] blkcg, btrfs: fix cgroup writeback support

The block part has already been applied to

  https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/ for-linus

with some naming changes.  This patchset has been updated accordingly.

When writeback is executed asynchronously (e.g. for compression), bios
are bounced to and issued by worker pool shared by all cgroups.  This
leads to significant priority inversions when cgroup IO control is in
use - IOs for a low priority cgroup can tie down the workers forcing
higher priority IOs to wait behind them.

This patchset updates btrfs to issue async IOs through the new bio
punt mechanism.  A bio tagged with REQ_CGROUP_PUNT flag is bounced to
the asynchronous issue context of the associated blkcg on
bio_submit().  As the bios are issued from per-blkcg work items,
there's no concern for priority inversions and it doesn't require
invasive changes to the filesystems.

This patchset contains the following 5 patches.

 0001-Btrfs-stop-using-btrfs_schedule_bio.patch
 0002-Btrfs-delete-the-entire-async-bio-submission-framewo.patch
 0003-Btrfs-only-associate-the-locked-page-with-one-async_.patch
 0004-Btrfs-use-REQ_CGROUP_PUNT-for-worker-thread-submitte.patch
 0005-Btrfs-extent_write_locked_range-should-attach-inode-.patch

The patches are also available in the following branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-btrfs-cgroup-updates-v3

Thanks, diffstat follows.

 fs/btrfs/compression.c |   16 ++
 fs/btrfs/compression.h |    3 
 fs/btrfs/ctree.h       |    1 
 fs/btrfs/disk-io.c     |   25 +---
 fs/btrfs/extent_io.c   |   15 +-
 fs/btrfs/inode.c       |   62 +++++++++--
 fs/btrfs/super.c       |    1 
 fs/btrfs/volumes.c     |  264 -------------------------------------------------
 fs/btrfs/volumes.h     |   10 -
 9 files changed, 90 insertions(+), 307 deletions(-)

--
tejun

[1] http://lkml.kernel.org/r/20190615182453.843275-1-tj@kernel.org