mm: try_to_free_swap replaces remove_exclusive_swap_page
commita2c43eed8334e878702fca713b212ae2a11d84b9
authorHugh Dickins <hugh@veritas.com>
Tue, 6 Jan 2009 22:39:36 +0000 (6 14:39 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 6 Jan 2009 23:59:03 +0000 (6 15:59 -0800)
tree4eb3f9b9153df5e7a638b15a6f7c9aa924066a94
parent7b1fe59793e61f826bef053107b57b23954833bb
mm: try_to_free_swap replaces remove_exclusive_swap_page

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>
include/linux/swap.h
mm/memory.c
mm/page_io.c
mm/swap.c
mm/swap_state.c
mm/swapfile.c
mm/vmscan.c