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Date: Mon, 13 Oct 2003 02:24:41 -0700
From: Andrew Morton <akpm@osdl.org>
To: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH][2.6] No swapping on memory backed swapfiles
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Zwane Mwaikambo <zwane@arm.linux.org.uk> wrote:
>
> On Mon, 13 Oct 2003, Andrew Morton wrote:
> 
> > Zwane Mwaikambo <zwane@arm.linux.org.uk> wrote:
> > >
> > > +	bdi = mapping->backing_dev_info;
> > >  +	if (bdi->memory_backed)
> > >  +		goto bad_swap;
> > >  +
> > 
> > I guess that makes sense, although someone might want to swap onto a
> > ramdisk-backed file just for some testing purpose.
> > 
> > Why not simply test for a null ->readpage()?
> 
> That was my initial intention, but then i wondered why someone would be 
> swapping to a memory backed filesystem in the first place. Also things 
> like ramfs have ->readpage().

A non-memory-backed fs may still have a NULL ->readpage though (ncpfs?).

I do think it best to just test for ->readpage, and give the user the extra
rope.