Re: [patch] CONFIG_ARCH_HAS_ATOMIC_UNSIGNED

[Andi Kleen <ak@suse.de>]

On Thu, Dec 16, 2004 at 04:44:20PM -0800, Dave Hansen wrote:
> 
> This reduces another one of the dependencies that struct page's
> definition has on any arch-specific header files.  Currently,
> only x86_64 uses this, so it's the only architecture that needed
> to be modified.

That's for page_flags_t, right?

I think it could be dropped right now and just use unsigned long for flags again. 

Since the objrmap work the saved 4 bytes in struct page are wasted in padding 
and I haven't found a way to use them for real space saving again
because all other members are 8 byte or paired 4 byte.

Of course if anybody could come up with a way to make struct page
smaller it would be very appreciated:

struct page {
        page_flags_t flags;             /* Atomic flags, some possibly
                                         * updated asynchronously */

			<------------ what to do with the 4 byte padding here?

        atomic_t _count;                /* Usage count, see below. */
        atomic_t _mapcount;             /* Count of ptes mapped in mms,
                                         * to show when page is mapped
                                         * & limit reverse map searches.
                                         */
        unsigned long private;          /* Mapping-private opaque data:
                                         * usually used for buffer_heads
                                         * if PagePrivate set; used for
                                         * swp_entry_t if PageSwapCache
                                         */
        struct address_space *mapping;  /* If low bit clear, points to
                                         * inode address_space, or NULL.
                                         * If page mapped as anonymous
                                         * memory, low bit is set, and
                                         * it points to anon_vma object:
                                         * see PAGE_MAPPING_ANON below.
                                         */
        pgoff_t index;                  /* Our offset within mapping. */
        struct list_head lru;           /* Pageout list, eg. active_list
                                         * protected by zone->lru_lock !
                                         */



-Andi
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