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mm: try_to_free_swap replaces remove_exclusive_swap_page

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remove_exclusive_swap_page(): its problem is in living up to its name.

It doesn't matter if someone else has a reference to the page (raised
page_count); it doesn't matter if the page is mapped into userspace
(raised page_mapcount - though that hints it may be worth keeping the
swap): all that matters is that there be no more references to the swap
(and no writeback in progress).

swapoff (try_to_unuse) has been removing pages from swapcache for years,
with no concern for page count or page mapcount, and we used to have a
comment in lookup_swap_cache() recognizing that: if you go for a page of
swapcache, you'll get the right page, but it could have been removed from
swapcache by the time you get page lock.

So, give up asking for exclusivity: get rid of
remove_exclusive_swap_page(), and remove_exclusive_swap_page_ref() and
remove_exclusive_swap_page_count() which were spawned for the recent LRU
work: replace them by the simpler try_to_free_swap() which just checks
page_swapcount().

Similarly, remove the page_count limitation from free_swap_and_count(),
but assume that it's worth holding on to the swap if page is mapped and
swap nowhere near full.  Add a vm_swap_full() test in free_swap_cache()?
It would be consistent, but I think we probably have enough for now.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: 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 14:39:36 -08:00
committed by Linus Torvalds
parent 7b1fe59793
commit a2c43eed83
7 changed files with 22 additions and 75 deletions
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10
include/linux/swap.h
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@@ -305,8 +305,7 @@ 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 reuse_swap_page(struct page *);
extern int remove_exclusive_swap_page(struct page *);
extern int remove_exclusive_swap_page_ref(struct page *);
extern int try_to_free_swap(struct page *);
struct backing_dev_info;
/* linux/mm/thrash.c */
@@ -388,12 +387,7 @@ static inline void delete_from_swap_cache(struct page *page)
#define reuse_swap_page(page) (page_mapcount(page) == 1)
static inline int remove_exclusive_swap_page(struct page *p)
{
return 0;
}
static inline int remove_exclusive_swap_page_ref(struct page *page)
static inline int try_to_free_swap(struct page *page)
{
return 0;
}