linux-kernel - Re: [PATCH 05/11] mm: swap: Implement generic handler for swap

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Date:	Thu, 3 May 2012 15:57:14 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
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>,
	David Miller <davem@...emloft.net>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Neil Brown <neilb@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Christie <michaelc@...wisc.edu>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH 05/11] mm: swap: Implement generic handler for
 swap_activate

On Tue, May 01, 2012 at 03:57:47PM -0700, Andrew Morton wrote:
> On Mon, 16 Apr 2012 13:17:49 +0100
> Mel Gorman <mgorman@...e.de> wrote:
> 
> > The version of swap_activate introduced is sufficient for swap-over-NFS
> > but would not provide enough information to implement a generic handler.
> > This patch shuffles things slightly to ensure the same information is
> > available for aops->swap_activate() as is available to the core.
> > 
> > No functionality change.
> > 
> > ...
> >
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -587,6 +587,8 @@ typedef struct {
> >  typedef int (*read_actor_t)(read_descriptor_t *, struct page *,
> >  		unsigned long, unsigned long);
> >  
> > +struct swap_info_struct;
> 
> Please put forward declarations at top-of-file.  To prevent accidental
> duplication later on.
> 

Done.

> >  struct address_space_operations {
> >  	int (*writepage)(struct page *page, struct writeback_control *wbc);
> >  	int (*readpage)(struct file *, struct page *);
> >
> > ...
> >
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> 
> Have you tested all this code with CONFIG_SWAP=n?
> 

Emm, it builds. That counts, right?

> Have you sought to minimise additional new code when CONFIG_SWAP=n?
> 

Not specifically, but generic_swapfile_activate() is defined in page_io.c
and that is built only if CONFIG_SWAP=y. Similarly swapon is in
swapfile.c which is only build when swap is enabled.

-- 
Mel Gorman
SUSE Labs
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