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mm: reuse_swap_page replaces can_share_swap_page

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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>
This commit is contained in:
Hugh Dickins
2009-01-06 14:39:34 -08:00
committed by Linus Torvalds
parent ab967d8601
commit 7b1fe59793
3 changed files with 15 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/swap.h
View File

@@ -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 map_swap_page(struct swap_info_struct *, pgoff_t);
extern sector_t swapdev_block(int, pgoff_t); extern sector_t swapdev_block(int, pgoff_t);
extern struct swap_info_struct *get_swap_info_struct(unsigned); 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(struct page *);
extern int remove_exclusive_swap_page_ref(struct page *); extern int remove_exclusive_swap_page_ref(struct page *);
struct backing_dev_info; struct backing_dev_info;
@@ -372,8 +372,6 @@ static inline struct page *lookup_swap_cache(swp_entry_t swp)
return NULL; 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, static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
gfp_t gfp_mask) 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) static inline int remove_exclusive_swap_page(struct page *p)
{ {

4
mm/memory.c
View File

@@ -1861,7 +1861,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
} }
page_cache_release(old_page); page_cache_release(old_page);
} }
reuse = can_share_swap_page(old_page); reuse = reuse_swap_page(old_page);
unlock_page(old_page); unlock_page(old_page);
} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) == } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
(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); inc_mm_counter(mm, anon_rss);
pte = mk_pte(page, vma->vm_page_prot); 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); pte = maybe_mkwrite(pte_mkdirty(pte), vma);
write_access = 0; write_access = 0;
} }

15
mm/swapfile.c
View File

@@ -326,17 +326,24 @@ static inline int page_swapcount(struct page *page)
} }
/* /*
* We can use this swap cache entry directly * We can write to an anon page without COW if there are no other references
* if there are no other references to it. * 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; int count;
VM_BUG_ON(!PageLocked(page)); VM_BUG_ON(!PageLocked(page));
count = page_mapcount(page); count = page_mapcount(page);
if (count <= 1 && PageSwapCache(page)) if (count <= 1 && PageSwapCache(page)) {
count += page_swapcount(page); count += page_swapcount(page);
if (count == 1 && !PageWriteback(page)) {
delete_from_swap_cache(page);
SetPageDirty(page);
}
}
return count == 1; return count == 1;
} }