From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH RFC 0/5] IO-less balance_dirty_pages() v2 (simple
 approach)
Date: Thu, 17 Mar 2011 11:51:39 -0400
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To: Curt Wohlgemuth <curtw@google.com>
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On Thu, Mar 17, 2011 at 08:46:23AM -0700, Curt Wohlgemuth wrote:
> But if one of one's goals is to provide some sort of disk isolation based on
> cgroup parameters, than having at most one stream of write requests
> effectively neuters the IO scheduler.

If you use any kind of buffered I/O you already fail in that respect.
Writeback from balance_dirty_page really is just the wort case right now
with more I/O supposed to be handled by the background threads.  So if
you want to implement isolation properly you need to track the
originator of the I/O between the copy to the pagecache and actual
writeback.