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

From: Nick Piggin
Date: Tue Jun 15 2010 - 07:20:28 EST

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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