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

Changes from v1[1]

* 0001-cgroup-blkcg-Prepare-some-symbols-for-module-and-CON.patch
added. It collects and adds symbol exports and dummy function def
to fix module and different config builds.

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 adds an bio punt mechanism to blkcg and updates btrfs to
issue async IOs through it. 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. The mechanism should be
generally useful for IO control support across different filesystems.

This patchset contains the following 9 patches. The first three are
my blkcg patches to implement the needed mechanisms. The latter five
are Chris Mason's btrfs cleanup and update patches. Please let me
know how the patches should be routed. Given that there currently
aren't other users, it's likely the easiest to route all through btrfs


0001-0003 implement wbc->no_wbc_acct, wbc_blkcg_css() and

0004-0007 are prep patches to simplify / improve async bio submission.

0008 makes btrfs use REQ_CGROUP_PUNT for async bios.

0009 fixes wbc writeback accounting for IOs issued through

This patchset is also available in the following git branch.

git:// review-btrfs-cgroup-updates-v2

Thanks, diffstat follows.

block/blk-cgroup.c | 54 +++++++++
block/blk-core.c | 3
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 | 61 ++++++++--
fs/btrfs/super.c | 1
fs/btrfs/volumes.c | 264 --------------------------------------------
fs/btrfs/volumes.h | 10 -
fs/fs-writeback.c | 5
include/linux/backing-dev.h | 1
include/linux/blk-cgroup.h | 16 ++
include/linux/blk_types.h | 10 +
include/linux/cgroup.h | 1
include/linux/writeback.h | 24 +++-
17 files changed, 198 insertions(+), 312 deletions(-)



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