Re: Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes

["Jan Beulich" <JBeulich@novell.com>]

>>> On 08.08.11 at 22:45, Dan Magenheimer <dan.magenheimer@oracle.com> wrote:
> From: Dan Magenheimer <dan.magenheimer@oracle.com>
> Subject: [PATCH V6 1/4] mm: frontswap: swap data structure changes
> 
> This first patch of four in the frontswap series makes available core
> swap data structures (swap_lock, swap_list and swap_info) that are
> needed by frontswap.c but we don't need to expose them to the dozens
> of files that include swap.h so we create a new swapfile.h just to
> extern-ify these.
> 
> Also add frontswap-related elements to swap_info_struct.  Frontswap_map
> points to vzalloc'ed one-bit-per-swap-page metadata that indicates
> whether the swap page is in frontswap or in the device and frontswap_pages
> counts how many pages are in frontswap.  We don't tie these to
> CONFIG_FRONTSWAP to avoid unnecessary clutter around various frontswap
> hooks.
> 
> [v6: rebase to 3.0-rc1]
> [v5: no change from v4]
> [v4: rebase to 2.6.39]
> Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
> Reviewed-by: Konrad Wilk <konrad.wilk@oracle.com>
> Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Matthew Wilcox <matthew@wil.cx>
> Cc: Chris Mason <chris.mason@oracle.com>
> Cc: Jan Beulich <JBeulich@novell.com>
> Cc: Rik Riel <riel@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> 
> --- linux/include/linux/swapfile.h	1969-12-31 17:00:00.000000000 -0700
> +++ frontswap/include/linux/swapfile.h	2011-08-08 08:59:03.951694506 -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/include/linux/swap.h	2011-08-08 08:19:25.880690134 -0600
> +++ frontswap/include/linux/swap.h	2011-08-08 08:59:03.952691415 -0600
> @@ -194,6 +194,8 @@ 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 */

#ifdef CONFIG_FRONTSWAP

> +	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
> +	unsigned int frontswap_pages;	/* frontswap pages in-use counter */


#endif

(to eliminate any overhead with that config option unset)

Jan

>  };
>  
>  struct swap_list_t {



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