linux-kernel - Re: [PATCH 00/14] Swap-over-NBD without deadlocking v5

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Message-ID: <20110715141021.GZ7529@suse.de>
Date:	Fri, 15 Jul 2011 15:10:21 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 00/14] Swap-over-NBD without deadlocking v5

On Thu, Jul 07, 2011 at 08:58:31AM -0400, Christoph Hellwig wrote:
> On Thu, Jul 07, 2011 at 10:47:37AM +0100, Mel Gorman wrote:
> > Additional complexity is required for swap-over-NFS but affects the
> > core kernel far less than this series. I do not have a series prepared
> > but from what's in a distro kernel, supporting NFS requires extending
> > address_space_operations for swapfile activation/deactivation with
> > some minor helpers and the bulk of the remaining complexity within
> > NFS itself.
> 
> The biggest addition for swap over NFS is to add proper support for
> a filesystem interface to do I/O on random kernel pages instead of
> the current nasty bmap hack the swapfile code is using. Splitting
> that work from all the required VM infrastructure should make life
> easier for everyone involved and allows merging it independeny as
> both bits have other uses case as well.
> 

The swap-over-nfs patches allows this possibility. There is a swapon
interface added that could be used by the filesystem to ensure the
underlying blocks are allocated and a swap_out/swap_in interface that
takes a struct file, struct page and writeback_control. This would
be an alternative to bmap being used to record the blocks backing
each extent.

Any objection to the swap-over-NBD stuff going ahead to get part of the
complexity out of the way?

-- 
Mel Gorman
SUSE Labs
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