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Date:   Fri, 14 Jun 2019 09:50:07 -0400
From:   Josef Bacik <josef@toxicpanda.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     dsterba@suse.com, clm@fb.com, josef@toxicpanda.com,
        axboe@kernel.dk, jack@suse.cz, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        kernel-team@fb.com
Subject: Re: [PATCH 7/8] Btrfs: use REQ_CGROUP_PUNT for worker thread
 submitted bios
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References: <20190614003350.1178444-1-tj@kernel.org>
 <20190614003350.1178444-8-tj@kernel.org>
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On Thu, Jun 13, 2019 at 05:33:49PM -0700, Tejun Heo wrote:
> From: Chris Mason <clm@fb.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@fb.com>
> Modified-and-reviewed-by: Tejun Heo <tj@kernel.org>
> ---

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

Thanks,

Josef