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

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Message-Id: <20100602122910.71f981e8.akpm@linux-foundation.org>
Date:	Wed, 2 Jun 2010 12:29:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
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

On Fri, 28 May 2010 10:40:41 -0700
Dan Magenheimer <dan.magenheimer@...cle.com> wrote:

> [PATCH V2 1/4] Frontswap (was Transcendent Memory): swap data structure changes
> 
> Core swap data structures are needed by frontswap.c but we don't
> need to expose them to the dozens of files that include swap.h
> so create a new swapfile.h just to extern-ify these.
> 
> Add frontswap-related elements to swap_info_struct.  Don't tie
> these to CONFIG_FRONTSWAP to avoid unnecessary clutter around
> various frontswap hooks.
> 
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> 
> Diffstat:
>  swap.h                                   |    2 ++
>  swapfile.h                               |   13 +++++++++++++
>  2 files changed, 15 insertions(+)
> 
> --- linux-2.6.34/include/linux/swapfile.h	1969-12-31 17:00:00.000000000 -0700
> +++ linux-2.6.34-frontswap/include/linux/swapfile.h	2010-05-21 16:36:45.000000000 -0600
> @@ -0,0 +1,13 @@
> +#ifndef _LINUX_SWAPFILE_H
> +#define _LINUX_SWAPFILE_H
> +
> +/*
> + * these were static in swapfile.c but frontswap.c needs them and we don't
> + * want to expose them to the dozens of source files that include swap.h
> + */
> +extern spinlock_t swap_lock;
> +extern struct swap_list_t swap_list;
> +extern struct swap_info_struct *swap_info[];
> +extern int try_to_unuse(unsigned int, bool, unsigned long);
> +
> +#endif /* _LINUX_SWAPFILE_H */
> --- 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.


>  };
>  
>  struct swap_list_t {
--
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