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

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Date:	Tue, 15 Jun 2010 21:20:18 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Evgeniy Polyakov <zbr@...emap.net>,
	Dave Chinner <david@...morbit.com>,
	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>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

On Tue, Jun 15, 2010 at 07:10:26AM -0400, Christoph Hellwig wrote:
> On Tue, Jun 15, 2010 at 08:55:38PM +1000, Nick Piggin wrote:
> > 
> > What I do in fsblock is to maintain a block-nr sorted tree of dirty
> > blocks. This works nicely because fsblock dirty state is properly
> > synchronized with page dirty state. So writeout can just walk this in
> > order and it provides pretty optimal submission pattern of any
> > interleavings of data and metadata. No need for buffer boundary or
> > hacks like that. (needs some intelligence for delalloc, though).
> 
> I think worrying about indirect blocks really doesn't matter much
> these days.  For one thing extent based filesystems have a lot less
> of these, and second for a journaling filesystem we only need to log
> modification to the indirect blocks and not actually write them back
> in place during the sync.  At least for XFS the actual writeback can
> happen a lot later, as part of the ordered list of delwri buffers.

That's true, more importantly I meant any interleavings of data from
more than one file too.

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