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

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [patch 3/4] mm: filemap: pass __GFP_WRITE from grab_cache_page_write_begin()
From: Johannes Weiner <jweiner@xxxxxxxxxx>
Date: Wed, 21 Sep 2011 16:09:35 +0200
Cc: Rik van Riel <riel@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>, Chris Mason <chris.mason@xxxxxxxxxx>, "Theodore Ts'o" <tytso@xxxxxxx>, Andreas Dilger <adilger.kernel@xxxxxxxxx>, xfs@xxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20110920184034.GA27353@xxxxxxxxxxxxx>
References: <1316526315-16801-1-git-send-email-jweiner@xxxxxxxxxx> <1316526315-16801-4-git-send-email-jweiner@xxxxxxxxxx> <20110920142553.GA2593@xxxxxxxxxxxxx> <4E78DD8B.1020605@xxxxxxxxxx> <20110920184034.GA27353@xxxxxxxxxxxxx>
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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