linux-kernel - RE: [PATCH V2 1/4] Frontswap (was Transcendent Memory): swap data structure changes

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Message-ID: <a9f0652d-7607-4e3f-a453-b37a1b0b4d94@default>
Date:	Wed, 2 Jun 2010 17:10:36 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hugh.dickins@...cali.co.uk, ngupta@...are.org, JBeulich@...ell.com,
	chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, npiggin@...e.de, riel@...hat.com,
	avi@...hat.com, pavel@....cz, konrad.wilk@...cle.com
Subject: RE: [PATCH V2 1/4] Frontswap (was Transcendent Memory): swap data
 structure changes

> > --- linux-2.6.34/include/linux/swap.h	2010-05-16 15:17:36.000000000
> -0600
> > +++ linux-2.6.34-frontswap/include/linux/swap.h	2010-05-24
> 10:13:41.000000000 -0600
> > @@ -182,6 +182,8 @@ struct swap_info_struct {
> >  	struct block_device *bdev;	/* swap device or bdev of swap file
> */
> >  	struct file *swap_file;		/* seldom referenced */
> >  	unsigned int old_block_size;	/* seldom referenced */
> > +	unsigned long *frontswap_map;	/* frontswap in-use, one bit per
> page */
> > +	unsigned int frontswap_pages;	/* frontswap pages in-use counter
> */
> 
> Is a 32-bit uint large enough?  Maybe there are other things in swap
> which restrict us to less than 16TB, dunno.

Yes, the same data structure has "unsigned int pages" which is
the "total of usable pages" in the swap device.  If/when
"pages" changes to an unsigned long (or long long), then
"frontswap_pages" should change also.

Thanks,
Dan
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