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blkcg: implement REQ_CGROUP_PUNT

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When a shared kthread needs to issue a bio for a cgroup, doing so
synchronously can lead to priority inversions as the kthread can be
trapped waiting for that cgroup.  This patch implements
REQ_CGROUP_PUNT flag which makes submit_bio() punt the actual issuing
to a dedicated per-blkcg work item to avoid such priority inversions.

This will be used to fix priority inversions in btrfs compression and
should be generally useful as we grow filesystem support for
comprehensive IO control.

Cc: Chris Mason <clm@fb.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo
2019-06-27 13:39:52 -07:00
committed by Jens Axboe
parent 653c45c6b9
commit d3f77dfdc7
6 changed files with 94 additions and 6 deletions
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include/linux/backing-dev.h
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@@ -48,6 +48,7 @@ extern spinlock_t bdi_lock;
extern struct list_head bdi_list;
extern struct workqueue_struct *bdi_wq;
extern struct workqueue_struct *bdi_async_bio_wq;
static inline bool wb_has_dirty_io(struct bdi_writeback *wb)
{