From: Minchan Kim <minchan@xxxxxxxxxx> Subject: mm: swap: SWP_SYNCHRONOUS_IO: skip swapcache only if swapped page has no other reference When SWP_SYNCHRONOUS_IO swapped-in pages are shared by several processes, it can cause unnecessary memory wastage by skipping swap cache. Because, with swapin fault by read, they could share a page if the page were in swap cache. Thus, it avoids allocating same content new pages. This patch makes the swapcache skipping work only if the swap pte is non-sharable. [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] Link: http://lkml.kernel.org/r/1507620825-5537-1-git-send-email-minchan@xxxxxxxxxx Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Ilya Dryomov <idryomov@xxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/swap.h | 6 ++++++ mm/memory.c | 19 ++++++++++--------- mm/swapfile.c | 7 +++++++ 3 files changed, 23 insertions(+), 9 deletions(-) diff -puN include/linux/swap.h~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference include/linux/swap.h --- a/include/linux/swap.h~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference +++ a/include/linux/swap.h @@ -463,6 +463,7 @@ extern unsigned int count_swap_pages(int extern sector_t map_swap_page(struct page *, struct block_device **); extern sector_t swapdev_block(int, pgoff_t); extern int page_swapcount(struct page *); +extern int __swap_count(struct swap_info_struct *si, swp_entry_t entry); extern int __swp_swapcount(swp_entry_t entry); extern int swp_swapcount(swp_entry_t entry); extern struct swap_info_struct *page_swap_info(struct page *); @@ -588,6 +589,11 @@ static inline int page_swapcount(struct { return 0; } + +static inline int __swap_count(struct swap_info_struct *si, swp_entry_t entry) +{ + return 0; +} static inline int __swp_swapcount(swp_entry_t entry) { diff -puN mm/memory.c~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference mm/memory.c --- a/mm/memory.c~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference +++ a/mm/memory.c @@ -2890,15 +2890,8 @@ int do_swap_page(struct vm_fault *vmf) if (!page) { struct swap_info_struct *si = swp_swap_info(entry); - if (!(si->flags & SWP_SYNCHRONOUS_IO)) { - if (vma_readahead) - page = do_swap_page_readahead(entry, - GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); - else - page = swapin_readahead(entry, - GFP_HIGHUSER_MOVABLE, vma, vmf->address); - swapcache = page; - } else { + if (si->flags & SWP_SYNCHRONOUS_IO && + __swap_count(si, entry) == 1) { /* skip swapcache */ page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address); if (page) { @@ -2908,6 +2901,14 @@ int do_swap_page(struct vm_fault *vmf) lru_cache_add_anon(page); swap_readpage(page, true); } + } else { + if (vma_readahead) + page = do_swap_page_readahead(entry, + GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); + else + page = swapin_readahead(entry, + GFP_HIGHUSER_MOVABLE, vma, vmf->address); + swapcache = page; } if (!page) { diff -puN mm/swapfile.c~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference mm/swapfile.c --- a/mm/swapfile.c~mm-swap-skip-swapcache-only-if-swapped-page-has-no-other-reference +++ a/mm/swapfile.c @@ -1328,6 +1328,13 @@ int page_swapcount(struct page *page) return count; } +int __swap_count(struct swap_info_struct *si, swp_entry_t entry) +{ + pgoff_t offset = swp_offset(entry); + + return swap_count(si->swap_map[offset]); +} + static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry) { int count = 0; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
