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SubjectRe: [PATCH 4/9] blkcg: implement REQ_CGROUP_PUNT

On Sat, Jun 15, 2019 at 11:24:48AM -0700, Tejun Heo wrote:
> 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.
> Signed-off-by: Tejun Heo <>
> Reviewed-by: Josef Bacik <>
> Cc: Chris Mason <>

The blkcg patches, especially this one, need Jens's review. Jens, if
you're okay with the changes, please let me know how you want them to
be routed.



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