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From: Andrea Righi <arighi@develer.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Balbir Singh <balbir@linux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Greg Thelen <gthelen@google.com>,
	Wu Fengguang <fengguang.wu@intel.com>,
	Gui Jianfeng <guijianfeng@cn.fujitsu.com>,
	Ryo Tsuruta <ryov@valinux.co.jp>,
	Hirokazu Takahashi <taka@valinux.co.jp>,
	Jens Axboe <axboe@kernel.dk>,
	Andrew Morton <akpm@linux-foundation.org>,
	containers@lists.linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/5] page_cgroup: make page tracking available for blkio
Date: Wed, 23 Feb 2011 00:37:18 +0100	[thread overview]
Message-ID: <20110222233718.GF23723@linux.develer.com> (raw)
In-Reply-To: <20110222230630.GL28269@redhat.com>

On Tue, Feb 22, 2011 at 06:06:30PM -0500, Vivek Goyal wrote:
> On Wed, Feb 23, 2011 at 12:01:47AM +0100, Andrea Righi wrote:
> > On Tue, Feb 22, 2011 at 01:01:45PM -0700, Jonathan Corbet wrote:
> > > On Tue, 22 Feb 2011 18:12:54 +0100
> > > Andrea Righi <arighi@develer.com> wrote:
> > > 
> > > > The page_cgroup infrastructure, currently available only for the memory
> > > > cgroup controller, can be used to store the owner of each page and
> > > > opportunely track the writeback IO. This information is encoded in
> > > > the upper 16-bits of the page_cgroup->flags.
> > > > 
> > > > A owner can be identified using a generic ID number and the following
> > > > interfaces are provided to store a retrieve this information:
> > > > 
> > > >   unsigned long page_cgroup_get_owner(struct page *page);
> > > >   int page_cgroup_set_owner(struct page *page, unsigned long id);
> > > >   int page_cgroup_copy_owner(struct page *npage, struct page *opage);
> > > 
> > > My immediate observation is that you're not really tracking the "owner"
> > > here - you're tracking an opaque 16-bit token known only to the block
> > > controller in a field which - if changed by anybody other than the block
> > > controller - will lead to mayhem in the block controller.  I think it
> > > might be clearer - and safer - to say "blkcg" or some such instead of
> > > "owner" here.
> > > 
> > 
> > Basically the idea here was to be as generic as possible and make this
> > feature potentially available also to other subsystems, so that cgroup
> > subsystems may represent whatever they want with the 16-bit token.
> > However, no more than a single subsystem may be able to use this feature
> > at the same time.
> > 
> > > I'm tempted to say it might be better to just add a pointer to your
> > > throtl_grp structure into struct page_cgroup.  Or maybe replace the
> > > mem_cgroup pointer with a single pointer to struct css_set.  Both of
> > > those ideas, though, probably just add unwanted extra overhead now to gain
> > > generality which may or may not be wanted in the future.
> > 
> > The pointer to css_set sounds good, but it would add additional space to
> > the page_cgroup struct. Now, page_cgroup is 40 bytes (in 64-bit arch)
> > and all of them are allocated at boot time. Using unused bits in
> > page_cgroup->flags is a choice with no overhead from this point of view.
> 
> I think John suggested replacing mem_cgroup pointer with css_set so that
> size of the strcuture does not increase but it leads extra level of 
> indirection.

OK, got it sorry.

So, IIUC we save css_set pointer and get a struct cgroup as following:

  struct cgroup *cgrp = css_set->subsys[subsys_id]->cgroup;

Then, for example to get the mem_cgroup reference:

  struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);

It seems a lot of indirections, but I may have done something wrong or
there could be a simpler way to do it.

Thanks,
-Andrea

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  parent reply	other threads:[~2011-02-22 23:37 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-22 17:12 [PATCH 0/5] blk-throttle: writeback and swap IO control Andrea Righi
2011-02-22 17:12 ` [PATCH 1/5] blk-cgroup: move blk-cgroup.h in include/linux/blk-cgroup.h Andrea Righi
2011-02-22 17:12 ` [PATCH 2/5] blk-cgroup: introduce task_to_blkio_cgroup() Andrea Righi
2011-02-22 17:12 ` [PATCH 3/5] page_cgroup: make page tracking available for blkio Andrea Righi
2011-02-22 20:01   ` Jonathan Corbet
2011-02-22 21:57     ` Vivek Goyal
2011-02-22 23:01     ` Andrea Righi
2011-02-22 23:06       ` Vivek Goyal
2011-02-22 23:21         ` Jonathan Corbet
2011-02-22 23:37         ` Andrea Righi [this message]
2011-02-23  4:49           ` KAMEZAWA Hiroyuki
2011-02-23  8:59             ` Andrea Righi
2011-02-23 23:58               ` KAMEZAWA Hiroyuki
2011-02-25  0:48                 ` Andrea Righi
2011-02-22 23:27       ` Jonathan Corbet
2011-02-22 23:48         ` Andrea Righi
2011-02-22 21:22   ` Vivek Goyal
2011-02-22 23:08     ` Andrea Righi
2011-02-22 17:12 ` [PATCH 4/5] blk-throttle: track buffered and anonymous pages Andrea Righi
2011-02-22 18:42   ` Chad Talbott
2011-02-22 19:12     ` Andrea Righi
2011-02-22 20:49     ` Vivek Goyal
2011-02-22 23:03       ` Andrea Righi
2011-02-22 21:00   ` Vivek Goyal
2011-02-22 23:05     ` Andrea Righi
2011-02-23  0:07       ` Vivek Goyal
2011-02-23  8:37         ` Andrea Righi
2011-02-22 17:12 ` [PATCH 5/5] blk-throttle: buffered and anonymous page tracking instrumentation Andrea Righi
2011-02-22 19:34 ` [PATCH 0/5] blk-throttle: writeback and swap IO control Vivek Goyal
2011-02-22 22:41   ` Andrea Righi
2011-02-23  0:03     ` Vivek Goyal
2011-02-23  8:32       ` Andrea Righi
2011-02-23 15:23         ` Vivek Goyal
2011-02-23 23:14           ` Andrea Righi
2011-02-24  0:10             ` Vivek Goyal
2011-02-24  0:40               ` KAMEZAWA Hiroyuki
2011-02-24  2:01                 ` Greg Thelen
2011-02-24 16:18                 ` Vivek Goyal
2011-02-25  0:54               ` Andrea Righi
2011-02-24  6:08 ` Balbir Singh

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