linux-kernel - Re: [PATCH 4/5] blk-throttle: track buffered and anonymous pages

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Date:	Tue, 22 Feb 2011 20:12:47 +0100
From:	Andrea Righi <arighi@...eler.com>
To:	Chad Talbott <ctalbott@...gle.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Greg Thelen <gthelen@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	Ryo Tsuruta <ryov@...inux.co.jp>,
	Hirokazu Takahashi <taka@...inux.co.jp>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] blk-throttle: track buffered and anonymous pages

On Tue, Feb 22, 2011 at 10:42:41AM -0800, Chad Talbott wrote:
> On Tue, Feb 22, 2011 at 9:12 AM, Andrea Righi <arighi@...eler.com> wrote:
> > Add the tracking of buffered (writeback) and anonymous pages.
> ...
> > ---
> >  block/blk-throttle.c   |   87 +++++++++++++++++++++++++++++++++++++++++++++++-
> >  include/linux/blkdev.h |   26 ++++++++++++++-
> >  2 files changed, 111 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> > index 9ad3d1e..a50ee04 100644
> > --- a/block/blk-throttle.c
> > +++ b/block/blk-throttle.c
> ...
> > +int blk_throtl_set_anonpage_owner(struct page *page, struct mm_struct *mm)
> > +int blk_throtl_set_filepage_owner(struct page *page, struct mm_struct *mm)
> > +int blk_throtl_copy_page_owner(struct page *npage, struct page *opage)
> 
> It would be nice if these were named blk_cgroup_*.  This is arguably
> more correct as the id comes from the blkio subsystem, and isn't
> specific to blk-throttle.  This will be more important very shortly,
> as CFQ will be using this same cgroup id for async IO tracking soon.

Sounds reasonable. Will do in the next version.

> 
> is_kernel_io() is a good idea, it avoids a bug that we've run into
> with CFQ async IO tracking.  Why isn't PF_KTHREAD sufficient to cover
> all kernel threads, including kswapd and those marked PF_MEMALLOC?

With PF_MEMALLOC we're sure we don't add the page tracking overhead also
to non-kernel threads when memory gets low.

PF_KSWAPD is not probably needed, AFAICS it is only used by kswapd, that
is created by kthread_create() and so it has the PF_KTHREAD flag set.

Let's see if someone can give more deatils about that. In the while I'll
investigate and try to do some tests only with PF_KTHREAD.

Thanks,
-Andrea
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