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| author | Hugh Dickins <hugh@veritas.com> | 2009-01-06 14:39:34 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-01-06 15:59:03 -0800 |
| commit | 7b1fe59793e61f826bef053107b57b23954833bb (patch) | |
| tree | 0ac769c48123c5d0770b0a0f88bad9e6318b83ed /mm | |
| parent | ab967d86015a19777955370deebc8262d50fed63 (diff) | |
| download | lwn-7b1fe59793e61f826bef053107b57b23954833bb.tar.gz lwn-7b1fe59793e61f826bef053107b57b23954833bb.zip | |
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 <hugh@veritas.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memory.c | 4 | ||||
| -rw-r--r-- | mm/swapfile.c | 15 |
2 files changed, 13 insertions, 6 deletions
diff --git a/mm/memory.c b/mm/memory.c index 3922ffcf3dff..8f471edcb985 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 214e90b94946..bfd4ee59cb88 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; } |