linux-ext4 - Re: [PATCH] ext4: Rework the ext4_da

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Date:	Fri, 1 Aug 2008 09:36:40 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Theodore Tso <tytso@....edu>
Cc:	cmm@...ibm.com, sandeen@...hat.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Rework the ext4_da_writepages

On Thu, Jul 31, 2008 at 11:08:25PM -0400, Theodore Tso wrote:
> On Thu, Jul 31, 2008 at 11:03:25PM +0530, Aneesh Kumar K.V wrote:
> > With the below changes we reserve credit needed to insert only one extent
> > resulting from a call to single get_block. That make sure we don't take
> > too much journal credits during writeout. We also don't limit the pages
> > to write. That means we loop through the dirty pages building largest
> > possible contiguous block request. Then we issue a single get_block request.
> > We may get less block that we requested. If so we would end up not mapping
> > some of the buffer_heads. That means those buffer_heads are still marked delay.
> > Later in the writepage callback via __mpage_writepage we redirty those pages.
> 
> If you're only redirtying the pages in the callback, that means they
> are left clean but with the delayed flag set; is that going to be
> enough to keep the mm from dropping the pages because they are clean?
> Or is the mechanism which prevents this is that you've kept the
> refcount on the pages bumped until after the callback?

writepages can use redirty_page_for_writepage to skip the pages during
writeout. We do that in most of the writepage call backs.
So I guess they would be properly marked dirty .

-aneesh
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