linux-kernel - Re: [PATCH 4/9] blkcg: implement REQ_CGROUP

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Message-ID: <20190615182933.GH657710@devbig004.ftw2.facebook.com>
Date:   Sat, 15 Jun 2019 11:29:33 -0700
From:   Tejun Heo <tj@...nel.org>
To:     dsterba@...e.com, clm@...com, josef@...icpanda.com,
        axboe@...nel.dk, jack@...e.cz
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 4/9] blkcg: implement REQ_CGROUP_PUNT

Hello,

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 <tj@...nel.org>
> Reviewed-by: Josef Bacik <josef@...icpanda.com>
> Cc: Chris Mason <clm@...com>

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.

Thanks.

-- 
tejun