mm: remove try_to_munlock from vmscan

An unfortunate feature of the Unevictable LRU work was that reclaiming an
anonymous page involved an extra scan through the anon_vma: to check that
the page is evictable before allocating swap, because the swap could not
be freed reliably soon afterwards.

Now try_to_free_swap() has replaced remove_exclusive_swap_page(), that's
not an issue any more: remove try_to_munlock() call from
shrink_page_list(), leaving it to try_to_munmap() to discover if the page
is one to be culled to the unevictable list - in which case then
try_to_free_swap().

Update unevictable-lru.txt to remove comments on the try_to_munlock() in
shrink_page_list(), and shorten some lines over 80 columns.

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>

1 files changed, 2 insertions, 9 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c8601dd36603..74f875733e2b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -625,15 +625,6 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                 if (PageAnon(page) && !PageSwapCache(page)) {
                         if (!(sc->gfp_mask & __GFP_IO))
                                 goto keep_locked;
-                        switch (try_to_munlock(page)) {
-                        case SWAP_FAIL:         /* shouldn't happen */
-                        case SWAP_AGAIN:
-                                goto keep_locked;
-                        case SWAP_MLOCK:
-                                goto cull_mlocked;
-                        case SWAP_SUCCESS:
-                                ; /* fall thru'; add to swap cache */
-                        }
                         if (!add_to_swap(page, GFP_ATOMIC))
                                 goto activate_locked;
                         may_enter_fs = 1;
@@ -752,6 +743,8 @@ free_it:
                 continue;
 
 cull_mlocked:
+                if (PageSwapCache(page))
+                        try_to_free_swap(page);
                 unlock_page(page);
                 putback_lru_page(page);
                 continue;