linux-kernel - Re: [PATCH 7/8] Btrfs: use REQ_CGROUP_PUNT for worker thread submitted bios

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Message-ID: <20190614135006.ug5qgpc5uocuip6b@MacBook-Pro-91.local>
Date:   Fri, 14 Jun 2019 09:50:07 -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 7/8] Btrfs: use REQ_CGROUP_PUNT for worker thread
 submitted bios

On Thu, Jun 13, 2019 at 05:33:49PM -0700, Tejun Heo wrote:
> From: Chris Mason <clm@...com>
> 
> Async CRCs and compression submit IO through helper threads, which
> means they have IO priority inversions when cgroup IO controllers are
> in use.
> 
> This flags all of the writes submitted by btrfs helper threads as
> REQ_CGROUP_PUNT.  submit_bio() will punt these to dedicated per-blkcg
> work items to avoid the priority inversion.
> 
> For the compression code, we take a reference on the wbc's blkg css and
> pass it down to the async workers.
> 
> For the async crcs, the bio already has the correct css, we just need to
> tell the block layer to use REQ_CGROUP_PUNT.
> 
> Signed-off-by: Chris Mason <clm@...com>
> Modified-and-reviewed-by: Tejun Heo <tj@...nel.org>
> ---

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

Thanks,

Josef