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

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Date:	Tue, 17 Aug 2010 10:41:40 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Peter Staubach <staubach@...hat.com>
Subject: Re: [RFC][PATCH] Per file dirty limit throttling

On Mon, Aug 16, 2010 at 12:19:50PM +0800, Nikanth Karthikesan wrote:
> When the total dirty pages exceed vm_dirty_ratio, the dirtier is made to do
> the writeback. But this dirtier may not be the one who took the system to this
> state. Instead, if we can track the dirty count per-file, we could throttle
> the dirtier of a file, when the file's dirty pages exceed a certain limit.
> Even though this dirtier may not be the one who dirtied the other pages of
> this file, it is fair to throttle this process, as it uses that file.

Nikanth, there's a more elegant solution in upstream kernel.
See the comment for task_dirty_limit() in commit 1babe1838.

NFS may want to limit per-file dirty pages, to prevent long stall time
inside the nfs_getattr()->filemap_write_and_wait() calls (and problems
like that). Peter Staubach has similar ideas on it.

Thanks,
Fengguang
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