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

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

[Dan Magenheimer]

[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@oracle.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 */
 };
 
 struct swap_list_t {

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

[Andrew Morton]

On Fri, 28 May 2010 10:40:41 -0700
Dan Magenheimer <dan.magenheimer@oracle.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@oracle.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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RE: [PATCH V2 1/4] Frontswap (was Transcendent Memory): swap data structure changes

[Dan Magenheimer]

> > --- 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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