netdev - Re: [PATCH 03/10] mm: Add support for a filesystem to control swap files

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Date:	Fri, 9 Sep 2011 09:00:08 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	Linux-NFS <linux-nfs@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 03/10] mm: Add support for a filesystem to control swap
 files

On Fri, Sep 09, 2011 at 12:00:47PM +0100, Mel Gorman wrote:
> Currently swapfiles are managed entirely by the core VM by using
> ->bmap to allocate space and write to the blocks directly. This
> patch adds address_space_operations methods that allow a filesystem
> to optionally control the swapfile.
> 
>   int swap_activate(struct file *);
>   int swap_deactivate(struct file *);
>   int swap_writepage(struct file *, struct page *, struct writeback_control *);
>   int swap_readpage(struct file *, struct page *);

Just as the last two dozen times this came up:

NAK

The right fix is to add a filesystem method to support direct-I/O on
arbitrary kernel pages, instead of letting the wap abstraction leak into
the filesystem.
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