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Date: Wed, 3 Aug 2011 10:18:07 -0400
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 3/8] ext4: Warn if direct reclaim tries to writeback pages
Message-ID: <20110803141807.GA7676@infradead.org>
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To: Johannes Weiner <jweiner@redhat.com>
Cc: Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>, LKML <linux-kernel@vger.kernel.org>, XFS <xfs@oss.sgi.com>, Christoph Hellwig <hch@infradead.org>, Linux-MM <linux-mm@kvack.org>, Mel Gorman <mgorman@suse.de>, Wu Fengguang <fengguang.wu@intel.com>, josef@redhat.com, Minchan Kim <minchan.kim@gmail.com>

On Wed, Aug 03, 2011 at 04:00:19PM +0200, Johannes Weiner wrote:
> > That said, in my current revision of the series, I've dropped these
> > patches altogether as page migration should be able to trigger the same
> > warnings but be called from paths that are of less concern for stack
> > overflows (or at the very least be looked at as a separate series).
> 
> Doesn't this only apply to btrfs which has no own .migratepage aop for
> file pages?  The others use buffer_migrate_page.
> 
> But if you dropped them anyway, it does not matter :)

Note that the mid-term plan is to kill ->writepage as an address space
method.  Besides the usage from reclaim as as callbacks to
write_cache_pages and write_one_page (which can be made explicit
arguments) the only remaining user is the above mentioned fallback.

Josef, any chance you could switch btrfs over to implement a proper
->migratepage?

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