From 7b1fe59793e61f826bef053107b57b23954833bb Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 6 Jan 2009 14:39:34 -0800 Subject: [PATCH] mm: reuse_swap_page replaces can_share_swap_page A good place to free up old swap is where do_wp_page(), or do_swap_page(), is about to redirty the page: the data on disk is then stale and won't be read again; and if we do decide to write the page out later, using the previous swap location makes an unnecessary disk seek very likely. So give can_share_swap_page() the side-effect of delete_from_swap_cache() when it safely can. And can_share_swap_page() was always a misleading name, the more so if it has a side-effect: rename it reuse_swap_page(). Irrelevant cleanup nearby: remove swap_token_default_timeout definition from swap.h: it's used nowhere. Signed-off-by: Hugh Dickins Cc: Lee Schermerhorn Acked-by: Rik van Riel Cc: Nick Piggin Cc: KAMEZAWA Hiroyuki Cc: Robin Holt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/swap.h | 6 ++---- mm/memory.c | 4 ++-- mm/swapfile.c | 15 +++++++++++---- 3 files changed, 15 insertions(+), 10 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 48f309dc5a0..366556c5b14 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -304,7 +304,7 @@ extern unsigned int count_swap_pages(int, int); extern sector_t map_swap_page(struct swap_info_struct *, pgoff_t); extern sector_t swapdev_block(int, pgoff_t); extern struct swap_info_struct *get_swap_info_struct(unsigned); -extern int can_share_swap_page(struct page *); +extern int reuse_swap_page(struct page *); extern int remove_exclusive_swap_page(struct page *); extern int remove_exclusive_swap_page_ref(struct page *); struct backing_dev_info; @@ -372,8 +372,6 @@ static inline struct page *lookup_swap_cache(swp_entry_t swp) return NULL; } -#define can_share_swap_page(p) (page_mapcount(p) == 1) - static inline int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) { @@ -388,7 +386,7 @@ static inline void delete_from_swap_cache(struct page *page) { } -#define swap_token_default_timeout 0 +#define reuse_swap_page(page) (page_mapcount(page) == 1) static inline int remove_exclusive_swap_page(struct page *p) { diff --git a/mm/memory.c b/mm/memory.c index 3922ffcf3df..8f471edcb98 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1861,7 +1861,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, } page_cache_release(old_page); } - reuse = can_share_swap_page(old_page); + reuse = reuse_swap_page(old_page); unlock_page(old_page); } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED))) { @@ -2392,7 +2392,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma, inc_mm_counter(mm, anon_rss); pte = mk_pte(page, vma->vm_page_prot); - if (write_access && can_share_swap_page(page)) { + if (write_access && reuse_swap_page(page)) { pte = maybe_mkwrite(pte_mkdirty(pte), vma); write_access = 0; } diff --git a/mm/swapfile.c b/mm/swapfile.c index 214e90b9494..bfd4ee59cb8 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -326,17 +326,24 @@ static inline int page_swapcount(struct page *page) } /* - * We can use this swap cache entry directly - * if there are no other references to it. + * We can write to an anon page without COW if there are no other references + * to it. And as a side-effect, free up its swap: because the old content + * on disk will never be read, and seeking back there to write new content + * later would only waste time away from clustering. */ -int can_share_swap_page(struct page *page) +int reuse_swap_page(struct page *page) { int count; VM_BUG_ON(!PageLocked(page)); count = page_mapcount(page); - if (count <= 1 && PageSwapCache(page)) + if (count <= 1 && PageSwapCache(page)) { count += page_swapcount(page); + if (count == 1 && !PageWriteback(page)) { + delete_from_swap_cache(page); + SetPageDirty(page); + } + } return count == 1; } -- 2.41.1