Commit 7b1fe597 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hugh@veritas.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: default avatarRik 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ab967d86

include/linux/swap.h

+2 −4
Original line number Diff line number Diff line
@@ -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)

{

mm/memory.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

	}

mm/swapfile.c

+11 −4
Original line number Diff line number Diff line
@@ -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;

}

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