From: Tejun Heo <tj@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>
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 14:03:51 -0800 [thread overview]
Message-ID: <20120217220351.GI29414@google.com> (raw)
In-Reply-To: <20120217213313.GG26620@redhat.com>
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.
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.
Thanks.
--
tejun
next prev parent reply other threads:[~2012-02-17 22:03 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 [this message]
2012-02-17 22:29 ` Vivek Goyal
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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