On Mon, Jun 03, 2013 at 01:02:04PM -0700, Dave Hansen wrote:
>
>From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
>This patch defers the destruction of swapcache-specific data in
>'struct page'. This simplifies the code because we do not have
>to keep extra copies of the data during the removal of a page
>from the swap cache.
>
>There are only two callers of swapcache_free() which actually
>pass in a non-NULL 'struct page'. Both of them (__remove_mapping
>and delete_from_swap_cache()) create a temporary on-stack
>'swp_entry_t' and set entry.val to page_private().
>
>They need to do this since __delete_from_swap_cache() does
>set_page_private(page, 0) and destroys the information.
>
>However, I'd like to batch a few of these operations on several
>pages together in a new version of __remove_mapping(), and I
>would prefer not to have to allocate temporary storage for each
>page. The code is pretty ugly, and it's a bit silly to create
>these on-stack 'swp_entry_t's when it is so easy to just keep the
>information around in 'struct page'.
>
>There should not be any danger in doing this since we are
>absolutely on the path of freeing these page. There is no
>turning back, and no other rerferences can be obtained after it
>comes out of the radix tree.
>
>Note: This patch is separate from the next one since it
>introduces the behavior change. I've seen issues with this patch
>by itself in various forms and I think having it separate like
>this aids bisection.
>
>Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>Acked-by: Mel Gorman <mgorman@xxxxxxx>
>Reviewed-by: Minchan Kin <minchan@xxxxxxxxxx>
Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
>---
>
> linux.git-davehans/mm/swap_state.c | 4 ++--
> linux.git-davehans/mm/vmscan.c | 2 ++
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
>diff -puN mm/swap_state.c~__delete_from_swap_cache-dont-clear-page-private mm/swap_state.c
>--- linux.git/mm/swap_state.c~__delete_from_swap_cache-dont-clear-page-private 2013-06-03 12:41:30.321703206 -0700
>+++ linux.git-davehans/mm/swap_state.c 2013-06-03 12:41:30.326703428 -0700
>@@ -148,8 +148,6 @@ void __delete_from_swap_cache(struct pag
> entry.val = page_private(page);
> address_space = swap_address_space(entry);
> radix_tree_delete(&address_space->page_tree, page_private(page));
>- set_page_private(page, 0);
>- ClearPageSwapCache(page);
> address_space->nrpages--;
> __dec_zone_page_state(page, NR_FILE_PAGES);
> INC_CACHE_INFO(del_total);
>@@ -226,6 +224,8 @@ void delete_from_swap_cache(struct page
> spin_unlock_irq(&address_space->tree_lock);
>
> swapcache_free(entry, page);
>+ set_page_private(page, 0);
>+ ClearPageSwapCache(page);
> page_cache_release(page);
> }
>
>diff -puN mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private mm/vmscan.c
>--- linux.git/mm/vmscan.c~__delete_from_swap_cache-dont-clear-page-private 2013-06-03 12:41:30.323703296 -0700
>+++ linux.git-davehans/mm/vmscan.c 2013-06-03 12:41:30.328703516 -0700
>@@ -494,6 +494,8 @@ static int __remove_mapping(struct addre
> __delete_from_swap_cache(page);
> spin_unlock_irq(&mapping->tree_lock);
> swapcache_free(swap, page);
>+ set_page_private(page, 0);
>+ ClearPageSwapCache(page);
> } else {
> void (*freepage)(struct page *);
>
>_
>
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