linux-kernel - Re: [PATCH 12/12] blkcg: kill the mind-bending blkg->dev

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 19 Jan 2012 11:46:41 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/12] blkcg: kill the mind-bending blkg->dev

On Thu, Jan 19, 2012 at 08:30:56AM -0800, Tejun Heo wrote:
> Hello,
> 
> On Thu, Jan 19, 2012 at 10:49:19AM -0500, Vivek Goyal wrote:
> > > Let stat and conf read functions get device name from
> > > blkg->q->backing_dev_info.dev and pass it down to printing functions
> > > and remove blkg->dev.
> > 
> > I think one of the reasons for not using blkg->q->backing_dev_info.dev was
> > that there were still drivers where multiple gendisks were sharing the
> > request queue.
> 
> Hmmm... is that relevant?  The configurations / stats are per
> cgroup-request_queue pair.  How does multiple genhd's sharing a queue
> make any difference?  Also, the fill_dev_details functions were using
> the same q->backing_dev_info to fill it in, so it's not like it was
> using anything different.

You are right. Looks like it should not make any difference. Also looks
like bdi->dev points to first disk on the queue and ignores later ones.

int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                const char *fmt, ...)
{       
        if (bdi->dev)   /* The driver needs to use separate queues per
device */
                return 0;
}

So if a queue is being shared by multiple disks, then any throttling rule
on the device will practically trated a rule on the queue and will be
effective on all the devices cumulatively. So sounds fine.

Thanks
Vivek
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/