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    SubjectRe: [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@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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