linux-ext4 - Re: [patch 3/4] mm: filemap: pass __GFP_WRITE from grab_cache_page_write

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Date:	Wed, 21 Sep 2011 16:09:35 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Dave Chinner <david@...morbit.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Minchan Kim <minchan.kim@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>, xfs@....sgi.com,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/4] mm: filemap: pass __GFP_WRITE from
 grab_cache_page_write_begin()

On Tue, Sep 20, 2011 at 02:40:34PM -0400, Christoph Hellwig wrote:
> On Tue, Sep 20, 2011 at 02:38:03PM -0400, Rik van Riel wrote:
> > On 09/20/2011 10:25 AM, Christoph Hellwig wrote:
> > >In addition to regular write shouldn't __do_fault and do_wp_page also
> > >calls this if they are called on file backed mappings?
> > 
> > Probably not do_wp_page since it always creates an
> > anonymous page, which are not very relevant to the
> > dirty page cache accounting.
> 
> Well, it doesn't always - but for the case where it doesn't we
> do not allocate a new page at all so you're right in the end :)

I think it could be useful to annotate write-fault allocations in
filemap_fault(), but these pages are mostly allocated in the readahead
code, so this could turn into a more invasive project.

It can be done incrementally, however, the series as it stands does
not require it to be useful.
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