SHM_LOCKED pages are unevictable

Shmem segments locked into memory via shmctl(SHM_LOCKED) should not be
kept on the normal LRU, since scanning them is a waste of time and might
throw off kswapd's balancing algorithms.  Place them on the unevictable
LRU list instead.

Use the AS_UNEVICTABLE flag to mark address_space of SHM_LOCKed shared
memory regions as unevictable.  Then these pages will be culled off the
normal LRU lists during vmscan.

Add new wrapper function to clear the mapping's unevictable state when/if
shared memory segment is munlocked.

Add 'scan_mapping_unevictable_page()' to mm/vmscan.c to scan all pages in
the shmem segment's mapping [struct address_space] for evictability now
that they're no longer locked.  If so, move them to the appropriate zone
lru list.

Changes depend on [CONFIG_]UNEVICTABLE_LRU.

[kosaki.motohiro@jp.fujitsu.com: revert shm change]
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index a2113044d20a..7edb4cbc29f9 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -232,12 +232,16 @@ static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
 
 #ifdef CONFIG_UNEVICTABLE_LRU
 extern int page_evictable(struct page *page, struct vm_area_struct *vma);
+extern void scan_mapping_unevictable_pages(struct address_space *);
 #else
 static inline int page_evictable(struct page *page,
                                                 struct vm_area_struct *vma)
 {
         return 1;
 }
+static inline void scan_mapping_unevictable_pages(struct address_space *mapping)
+{
+}
 #endif
 
 extern int kswapd_run(int nid);