From: Vivek Goyal <vgoyal@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org,
Kent Overstreet <koverstreet@google.com>
Subject: Re: [PATCH 7/9] block: implement bio_associate_current()
Date: Fri, 17 Feb 2012 17:29:09 -0500 [thread overview]
Message-ID: <20120217222909.GI26620@redhat.com> (raw)
In-Reply-To: <20120217220351.GI29414@google.com>
On Fri, Feb 17, 2012 at 02:03:51PM -0800, Tejun Heo wrote:
> Hello, Vivek.
>
> On Fri, Feb 17, 2012 at 04:33:13PM -0500, Vivek Goyal wrote:
> > On Thu, Feb 16, 2012 at 02:37:56PM -0800, Tejun Heo wrote:
> >
> > [..]
> > > This patch implements bio_associate_current() which associates the
> > > specified bio with %current. The bio will record the associated ioc
> > > and blkcg at that point and block layer will use the recorded ones
> > > regardless of which task actually ends up issuing the bio. bio
> > > release puts the associated ioc and blkcg.
> >
> > How about storing blkcg information in io_context instead of bio. We will
> > have less copies of bio pointers and I think logically it makes sense.
>
> I don't know. The problem with that approach is that we introduce a
> persistent state which needs to be kept in sync. cgroup is a task
> property and the current code just grabs the current cgroup of
> %current and uses it for that bio. It doesn't matter how the task
> changes its cgroup membership later - we're correct (in a sense) no
> matter what. If we add cgroup pointer to ioc, we need to keep that in
> sync with task changing cgroup memberships and need to introduce
> synchronization scheme for accessing ioc->blkcg, which is a much
> bigger headache.
Don't we already keep track of task changing cgroup and record that
state in ioc.
blkiocg_attach()
ioc_cgroup_changed()
I think in ioc_cgroup_changed() we can just drop the reference to previous
blkcg and store reference to new blkcg?
>
> I think it's better to take an explicit ref now. If the situation
> changes, it's an implementation detail only known to block layer
> proper anyway, so we should be able to change it without too much
> difficulty.
I am fine with changing it later too.
BTW, this change seems to be completely orthogonal to blkcg cleanup. May
be it is a good idea to split it out in a separate patch series. It has
nothing to do with rcu cleanup in blkcg.
Thanks
Vivek
next prev parent reply other threads:[~2012-02-17 22:29 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-16 22:37 [PATCHSET] blkcg: update locking and fix stacking Tejun Heo
2012-02-16 22:37 ` [PATCH 1/9] blkcg: use double locking instead of RCU for blkg synchronization Tejun Heo
2012-02-16 22:37 ` [PATCH 2/9] blkcg: drop unnecessary RCU locking Tejun Heo
2012-02-17 16:19 ` Vivek Goyal
2012-02-17 17:07 ` Tejun Heo
2012-02-17 17:14 ` Tejun Heo
2012-02-17 16:47 ` Vivek Goyal
2012-02-17 17:11 ` Tejun Heo
2012-02-17 17:28 ` Vivek Goyal
2012-02-17 17:43 ` Tejun Heo
2012-02-17 18:08 ` Vivek Goyal
2012-02-17 18:16 ` Tejun Heo
2012-02-22 0:49 ` [PATCH UPDATED " Tejun Heo
2012-02-16 22:37 ` [PATCH 3/9] block: restructure get_request() Tejun Heo
2012-02-16 22:37 ` [PATCH 4/9] block: interface update for ioc/icq creation functions Tejun Heo
2012-02-16 22:37 ` [PATCH 5/9] block: ioc_task_link() can't fail Tejun Heo
2012-02-17 20:41 ` Vivek Goyal
2012-02-17 22:18 ` Tejun Heo
2012-02-16 22:37 ` [PATCH 6/9] block: add io_context->active_ref Tejun Heo
2012-02-16 22:37 ` [PATCH 7/9] block: implement bio_associate_current() Tejun Heo
2012-02-17 1:19 ` Kent Overstreet
2012-02-17 22:14 ` Tejun Heo
2012-02-17 22:34 ` Vivek Goyal
2012-02-17 22:41 ` Tejun Heo
2012-02-17 22:51 ` Vivek Goyal
2012-02-17 22:57 ` Tejun Heo
2012-02-20 14:22 ` Vivek Goyal
2012-02-20 16:59 ` Tejun Heo
2012-02-20 19:14 ` Vivek Goyal
2012-02-20 21:21 ` Tejun Heo
2012-02-27 23:12 ` Chris Wright
2012-02-28 14:10 ` Vivek Goyal
2012-02-28 17:01 ` Chris Wright
2012-02-28 20:11 ` Stefan Hajnoczi
2012-02-20 14:36 ` Vivek Goyal
2012-02-20 17:01 ` Tejun Heo
2012-02-20 19:16 ` Vivek Goyal
2012-02-20 21:06 ` Tejun Heo
2012-02-20 21:10 ` Vivek Goyal
2012-02-17 22:56 ` Vivek Goyal
2012-02-17 23:06 ` Tejun Heo
2012-02-17 21:33 ` Vivek Goyal
2012-02-17 22:03 ` Tejun Heo
2012-02-17 22:29 ` Vivek Goyal [this message]
2012-02-17 22:38 ` Tejun Heo
2012-02-17 22:42 ` Tejun Heo
2012-02-16 22:37 ` [PATCH 8/9] block: make block cgroup policies follow bio task association Tejun Heo
2012-02-16 22:37 ` [PATCH 9/9] block: make blk-throttle preserve the issuing task on delayed bios Tejun Heo
2012-02-17 21:58 ` Vivek Goyal
2012-02-17 22:17 ` Tejun Heo
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