linux-kernel - Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

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Message-ID: <4C16D46D.3020302@redhat.com>
Date:	Mon, 14 Jun 2010 21:16:29 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Dave Chinner <david@...morbit.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

On 06/14/2010 08:39 PM, Dave Chinner wrote:
> On Mon, Jun 14, 2010 at 04:21:43PM -0700, Andrew Morton wrote:

>> But then, this all really should be done at the block layer so other
>> io-submitting-paths can benefit from it.
>
> That was what we did in the past with really, really deep IO
> scheduler queues. That leads to IO latency and OOM problems because
> we could lock gigabytes of memory away under IO and take minutes to
> clean it.
>
> Besides, there really isn't the right context in the block layer to
> be able to queue and prioritise large amounts of IO without
> significant penalties to some higher layer operation.

Can we kick flushing for the whole inode at once from
vmscan.c?

That way we should:
1) ensure that the page we want is written to disk, and
2) we flush out related pages at the same time, getting
    a decent IO pattern

Chances are that if we want to evict one page from a
file, we'll also want to evict other pages from that
same file.  In fact, chances are a good number of them
will live nearby on the LRU list.

Does this make sense?

Would it be hard to add a "please flush this file"
way to call the filesystem flushing threads?

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