linux-kernel - Re: [PATCH 02/15] blkcg: delay blkg destruction until after writeback has finished

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Message-ID: <20180831201909.GA20194@dennisz-mbp.dhcp.thefacebook.com>
Date:   Fri, 31 Aug 2018 16:19:10 -0400
From:   Dennis Zhou <dennisszhou@...il.com>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>, kernel-team@...com,
        linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jiufei Xue <jiufei.xue@...ux.alibaba.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>
Subject: Re: [PATCH 02/15] blkcg: delay blkg destruction until after
 writeback has finished

Hi Josef,

On Fri, Aug 31, 2018 at 11:27:07AM -0400, Josef Bacik wrote:
> So the general approach is correct, but it's sort of confusing because you are
> using nr_cgwbs as a reference counter, because it's set at 1 at blkg creation
> time regardless of wether or not there's an assocated wb cg.  So instead why not
> just have a refcount_t ref, set it to 1 on creation and make the wb cg take a
> ref when it's attached, and then just do the get/put like normal and cleanup as
> you have below?  What you are doing is a reference counter masquerading as a
> count of the wb cg's, just add full ref counting to the blkcg and call it a day,
> it'll be much less confusing.  Thanks,

Yeah, that makes more sense. I've switched to using refcount_t and
renamed it to wbcg_refcnt. The corresponding actions have been renamed.

I've also fixed the kbuild error in v2.

Thanks,
Dennis