linux-kernel - Re: [PATCH 3/8] blkcg: implement REQ_CGROUP

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Message-ID: <20190614134342.rtm4iwxgzbsueyfg@MacBook-Pro-91.local>
Date:   Fri, 14 Jun 2019 09:43:43 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     dsterba@...e.com, clm@...com, josef@...icpanda.com,
        axboe@...nel.dk, jack@...e.cz, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 3/8] blkcg: implement REQ_CGROUP_PUNT

On Thu, Jun 13, 2019 at 05:33:45PM -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>
> Cc: Chris Mason <clm@...com>

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef