On Fri, May 31, 2013 at 11:38:56AM -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 Kim <minchan@xxxxxxxxxx> Look at below nitpick. > --- > > 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 2013-05-30 16:07:50.630079404 -0700 > +++ linux.git-davehans/mm/swap_state.c 2013-05-30 16:07:50.635079624 -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 2013-05-30 16:07:50.632079492 -0700 > +++ linux.git-davehans/mm/vmscan.c 2013-05-30 16:07:50.637079712 -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); It it worth to support non-atomic version of ClearPageSwapCache? -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>