linux-kernel - Re: [PATCH 0/6] buffered write IO controller in balance_dirty

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Message-ID: <20120401083030.GA5326@localhost>
Date:	Sun, 1 Apr 2012 01:30:30 -0700
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Suresh Jayaraman <sjayaraman@...e.com>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andrea Righi <andrea@...terlinux.com>,
	Jeff Moyer <jmoyer@...hat.com>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/6] buffered write IO controller in balance_dirty_pages()

On Sun, Apr 01, 2012 at 09:46:06AM +0530, Suresh Jayaraman wrote:
> On 03/28/2012 05:43 PM, Fengguang Wu wrote:
> > Here is one possible solution to "buffered write IO controller", based on Linux
> > v3.3
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux.git  buffered-write-io-controller
> > 
> 
> The implementation looks unbelievably simple. I ran a few tests
> (throttling) and I found it working well generally.

Thanks for test it out :)

> > Features:
> > - support blkio.weight
> > - support blkio.throttle.buffered_write_bps
> > 
> > Possibilities:
> > - it's trivial to support per-bdi .weight or .buffered_write_bps
> > 
> > Pros:
> > 1) simple
> > 2) virtually no space/time overheads
> > 3) independent of the block layer and IO schedulers, hence
> > 3.1) supports all filesystems/storages, eg. NFS/pNFS, CIFS, sshfs, ...
> > 3.2) supports all IO schedulers. One may use noop for SSDs, inside virtual machines, over iSCSI, etc.
> > 
> > Cons:
> > 1) don't try to smooth bursty IO submission in the flusher thread (*)
> > 2) don't support IOPS based throttling
> > 3) introduces semantic differences to blkio.weight, which will be
> >    - working by "bandwidth" for buffered writes
> >    - working by "device time" for direct IO
> 
> There is a chance that this semantic difference might confuse users.

Yeah.

> > (*) Maybe not a big concern, since the bursties are limited to 500ms: if one dd
> > is throttled to 50% disk bandwidth, the flusher thread will be waking up on
> > every 1 second, keep the disk busy for 500ms and then go idle for 500ms; if
> > throttled to 10% disk bandwidth, the flusher thread will wake up on every 5s,
> > keep busy for 500ms and stay idle for 4.5s.
> > 
> > The test results included in the last patch look pretty good in despite of the
> > simple implementation.
> > 
> >  [PATCH 1/6] blk-cgroup: move blk-cgroup.h in include/linux/blk-cgroup.h
> >  [PATCH 2/6] blk-cgroup: account dirtied pages
> >  [PATCH 3/6] blk-cgroup: buffered write IO controller - bandwidth weight
> >  [PATCH 4/6] blk-cgroup: buffered write IO controller - bandwidth limit
> >  [PATCH 5/6] blk-cgroup: buffered write IO controller - bandwidth limit interface
> >  [PATCH 6/6] blk-cgroup: buffered write IO controller - debug trace
> > 
> 
> How about a BOF on this topic during LSF/MM as there seems to be enough
> interest?

Sure. I'll talk briefly about the block IO cgroup in the writeback
session. I'm open to more oriented technical discussions in some later
time if necessary.

Thanks,
Fengguang
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