linux-kernel - Re: [PATCH 5/7] kiothrottled: throttle buffered (writeback) IO

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Date:	Thu, 23 Apr 2009 15:53:51 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Andrea Righi <righi.andrea@...il.com>
CC:	Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	agk@...rceware.org, akpm@...ux-foundation.org, axboe@...nel.dk,
	baramsori72@...il.com, Carl Henrik Lunde <chlunde@...g.uio.no>,
	dave@...ux.vnet.ibm.com, Divyesh Shah <dpshah@...gle.com>,
	eric.rannaud@...il.com, fernando@....ntt.co.jp,
	Hirokazu Takahashi <taka@...inux.co.jp>,
	Li Zefan <lizf@...fujitsu.com>, matt@...ehost.com,
	dradford@...ehost.com, ngupta@...gle.com, randy.dunlap@...cle.com,
	roberto@...it.it, Ryo Tsuruta <ryov@...inux.co.jp>,
	Satoshi UCHIDA <s-uchida@...jp.nec.com>,
	subrata@...ux.vnet.ibm.com, yoshikawa.takuya@....ntt.co.jp,
	Nauman Rafique <nauman@...gle.com>, fchecconi@...il.com,
	paolo.valente@...more.it, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] kiothrottled: throttle buffered (writeback) IO

Andrea Righi wrote:
> Together with cgroup_io_throttle() the kiothrottled kernel thread
> represents the core of the io-throttle subsystem.
> 
> All the writeback IO requests that need to be throttled are not
> dispatched immediately in submit_bio(). Instead, they are added into an
> rbtree by iothrottle_make_request() and processed asynchronously by
> kiothrottled.
> 
> A deadline is associated to each request depending on the bandwidth
> usage of the cgroup it belongs. When a request is inserted into the
> rbtree kiothrottled is awakened. This thread selects all the requests
> with an expired deadline and submit the bunch of selected requests to
> the underlying block devices using generic_make_request().

  Hi Andrea,

  What if an user issues "sync", will the bios still be buffered in the rb-tree?
  Do we need to flush the whole tree?

-- 
Regards
Gui Jianfeng

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