linux-kernel - Re: [RFC][PATCH] Per file dirty limit throttling

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Date:	Tue, 17 Aug 2010 10:24:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Bill Davidsen <davidsen@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [RFC][PATCH] Per file dirty limit throttling

On Tue, 2010-08-17 at 10:39 +0530, Nikanth Karthikesan wrote:
> Oh, nice.  Per-task limit is an elegant solution, which should help during 
> most of the common cases.
> 
> But I just wonder what happens, when
> 1. The dirtier is multiple co-operating processes
> 2. Some app like a shell script, that repeatedly calls dd with seek and skip? 
> People do this for data deduplication, sparse skipping etc..
> 3. The app dies and comes back again. Like a VM that is rebooted, and 
> continues writing to a disk backed by a file on the host.
> 
> Do you think, in those cases this might still be useful? 

Those cases do indeed defeat the current per-task-limit, however I think
the solution to that is to limit the amount of writeback done by each
blocked process.

Jan Kara had some good ideas in that department.
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