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/mm/shmem.c b/mm/shmem.c
index fc2ccf79a776..d38d7e61fcd0 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1477,12 +1477,16 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
                 if (!user_shm_lock(inode->i_size, user))
                         goto out_nomem;
                 info->flags |= VM_LOCKED;
+                mapping_set_unevictable(file->f_mapping);
         }
         if (!lock && (info->flags & VM_LOCKED) && user) {
                 user_shm_unlock(inode->i_size, user);
                 info->flags &= ~VM_LOCKED;
+                mapping_clear_unevictable(file->f_mapping);
+                scan_mapping_unevictable_pages(file->f_mapping);
         }
         retval = 0;
+
 out_nomem:
         spin_unlock(&info->lock);
         return retval;