linux-ext4 - Re: [PATCH updated] ext4: Fix file fragmentation during large file write.

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Date:	Sun, 12 Oct 2008 00:37:13 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	cmm@...ibm.com, tytso@....edu, sandeen@...hat.com,
	chris.mason@...cle.com, akpm@...ux-foundation.org,
	hch@...radead.org, steve@...gwyn.com, mpatocka@...hat.com,
	linux-mm@...ck.org, inux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH updated] ext4: Fix file fragmentation during large file
	write.

On Sat, Oct 11, 2008 at 11:44:26PM +0530, Aneesh Kumar K.V wrote:
> On Sat, Oct 11, 2008 at 12:51:52PM +0200, Nick Piggin wrote:
> > On Fri, Oct 10, 2008 at 11:32:56PM +0530, Aneesh Kumar K.V wrote:
> > > The range_cyclic writeback mode use the address_space
> > > writeback_index as the start index for writeback. With
> > > delayed allocation we were updating writeback_index
> > > wrongly resulting in highly fragmented file. Number of
> > > extents reduced from 4000 to 27 for a 3GB file with
> > > the below patch.
> > > 
> > > The patch also removes the range_cont writeback mode
> > > added for ext4 delayed allocation. Instead we add
> > > two new flags in writeback_control which control
> > > the behaviour of write_cache_pages.
> > 
> > The mm/page-writeback.c changes look OK, although it loks like you've
> > got rid of range_cont? Should we do a patch to get rid of it entirely
> > from the tree first?
> > 
> > I don't mind rediffing my patchset on top of this, but this seems smaller
> > and not strictly a bugfix so I would prefer to go the other way if you
> > agree.
> > 
> > Seems like it could be broken up into several patches (eg. pagevec_lookup).
> > 
> > The results look very nice.
> 
> I actually tried to do that. But to do that and also achieve a working
> bisect kernel, I will have to do the patches in below way
> 
> a) Introduce ext4_write_cache_pages
> b) remove range_cont from write_cache_pages
> c) Introduce the new flags to writeback_control
> d) switch ext4 to use write_cache_pages.
> 
> I thought that involved lot of code which are later getting removed.
> So i went for a single patch.
> 

Ok I did the split as below.

a) ext4: Use tag dirty lookup during mpage_da_submit_io
b) vfs: Remove the range_cont writeback mode.
c) vfs: Add no_nrwrite_update and no_index_update writeback control flags
d) ext4: Fix file fragmentation during large file write.

I have sent the updated patches to ext4 list and also to you. Let me
know what you think. The final change is same as the old patch. So
no new changes added

-aneesh

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