linux-kernel - Re: [PATCH 02/10] Common flat fair queuing code in elevaotor layer

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Message-ID: <20090402135202.GB12851@redhat.com>
Date:	Thu, 2 Apr 2009 09:52:02 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Divyesh Shah <dpshah@...gle.com>
Cc:	nauman@...gle.com, lizf@...fujitsu.com, mikew@...gle.com,
	fchecconi@...il.com, paolo.valente@...more.it,
	jens.axboe@...cle.com, ryov@...inux.co.jp,
	fernando@...ellilink.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com,
	arozansk@...hat.com, jmoyer@...hat.com, oz-kernel@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	menage@...gle.com, peterz@...radead.org
Subject: Re: [PATCH 02/10] Common flat fair queuing code in elevaotor layer

On Wed, Apr 01, 2009 at 09:06:40PM -0700, Divyesh Shah wrote:
> On Wed, Mar 11, 2009 at 6:56 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> > +/*
> > + * elv_exit_fq_data is called before we call elevator_exit_fn. Before
> > + * we ask elevator to cleanup its queues, we do the cleanup here so
> > + * that all the group and idle tree references to ioq are dropped. Later
> > + * during elevator cleanup, ioc reference will be dropped which will lead
> > + * to removal of ioscheduler queue as well as associated ioq object.
> > + */
> > +void elv_exit_fq_data(struct elevator_queue *e)
> > +{
> > +       struct elv_fq_data *efqd = &e->efqd;
> > +       struct request_queue *q = efqd->queue;
> > +
> > +       if (!elv_iosched_fair_queuing_enabled(e))
> > +               return;
> > +
> > +       elv_shutdown_timer_wq(e);
> > +
> > +       spin_lock_irq(q->queue_lock);
> > +       /* This should drop all the idle tree references of ioq */
> > +       elv_free_idle_ioq_list(e);
> > +       spin_unlock_irq(q->queue_lock);
> > +
> > +       elv_shutdown_timer_wq(e);
> > +
> > +       BUG_ON(timer_pending(&efqd->idle_slice_timer));
> > +       io_free_root_group(e);
> > +}
> >
> 
> Hi Vivek,
>         When cleaning up the elv_fq_data and ioqs for the iogs
> associated with a device on elv_exit(), I don't see any iogs except
> the root group being freed. In io_disconnect_groups() you remove the
> ioqs from each of the iog and move them to the root iog and then
> delete the root iog. Am I missing something here or are there leftover
> iogs at elv_exit?

Hi Divyesh,

io_groups are linked in two lists. One list is maintained by io_cgroup
to keep track of how many io_groups are there associated with this
cgroup and other list is maintained in elv_fq_data to keep track of
how many io_groups are actually doing IO to this device.

Upon elevator exit, we remove the io_groups (io_disconnect_groups())from the
list maintained by elv_fq_data but we don't free them up. Freeing up is
finally done when cgroup is being deleted (iocg_destroy()).

Thanks
Vivek
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