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Date: Fri, 14 Apr 2006 12:15:37 -0700
From: Andrew Morton <akpm@osdl.org>
To: Christoph Lameter <clameter@sgi.com>
Cc: hugh@veritas.com, linux-kernel@vger.kernel.org, lee.schermerhorn@hp.com,
       linux-mm@kvack.org, taka@valinux.co.jp, marcelo.tosatti@cyclades.com,
       kamezawa.hiroyu@jp.fujitsu.com
Subject: Re: Implement lookup_swap_cache for migration entries
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Christoph Lameter <clameter@sgi.com> wrote:
>
> On Fri, 14 Apr 2006, Andrew Morton wrote:
> 
> > > @@ -305,6 +306,12 @@ struct page * lookup_swap_cache(swp_entr
> > >  {
> > >  	struct page *page;
> > >  
> > > +	if (is_migration_entry(entry)) {
> > > +		page = migration_entry_to_page(entry);
> > > +		get_page(page);
> > > +		return page;
> > > +	}
> > 
> > What locking ensures that the state of `entry' remains unaltered across the
> > is_migration_entry() and migration_entry_to_page() calls?
> 
> entry is a variable passed by value to the function.

Sigh.

What locking ensures that the state of the page referred to by `entry' is
stable?