linux-kernel - Re: [PATCH 01/13] block: add bi

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Message-ID: <20180530154933.GI1351649@devbig577.frc2.facebook.com>
Date:   Wed, 30 May 2018 08:49:33 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     axboe@...nel.dk, kernel-team@...com, linux-block@...r.kernel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org, hannes@...xchg.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Josef Bacik <jbacik@...com>
Subject: Re: [PATCH 01/13] block: add bi_blkg to the bio for cgroups

On Tue, May 29, 2018 at 05:17:12PM -0400, Josef Bacik wrote:
> From: Josef Bacik <jbacik@...com>
> 
> Currently io.low uses a bi_cg_private to stash its private data for the
> blkg, however other blkcg policies may want to use this as well.  Since
> we can get the private data out of the blkg, move this to bi_blkg in the
> bio and make it generic, then we can use bio_associate_blkg() to attach
> the blkg to the bio.
> 
> Theoretically we could simply replace the bi_css with this since we can
> get to all the same information from the blkg, however you have to
> lookup the blkg, so for example wbc_init_bio() would have to lookup and
> possibly allocate the blkg for the css it was trying to attach to the
> bio.  This could be problematic and result in us either not attaching
> the css at all to the bio, or falling back to the root blkcg if we are
> unable to allocate the corresponding blkg.
> 
> So for now do this, and in the future if possible we could just replace
> the bi_css with bi_blkg and update the helpers to do the correct
> translation.
> 
> Signed-off-by: Josef Bacik <jbacik@...com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun