path: root/ipc/shm.c
diff options
authorHugh Dickins <hughd@google.com>2012-01-20 14:34:19 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-23 08:38:48 -0800
commit85046579bde15e532983438f86b36856e358f417 (patch)
tree9b80b31791e63520277617a5abe85692dc480cd0 /ipc/shm.c
parentcb78edfdcef5259ac9e9088bd63810d21299928d (diff)
SHM_UNLOCK: fix long unpreemptible section
scan_mapping_unevictable_pages() is used to make SysV SHM_LOCKed pages evictable again once the shared memory is unlocked. It does this with pagevec_lookup()s across the whole object (which might occupy most of memory), and takes 300ms to unlock 7GB here. A cond_resched() every PAGEVEC_SIZE pages would be good. However, KOSAKI-san points out that this is called under shmem.c's info->lock, and it's also under shm.c's shm_lock(), both spinlocks. There is no strong reason for that: we need to take these pages off the unevictable list soonish, but those locks are not required for it. So move the call to scan_mapping_unevictable_pages() from shmem.c's unlock handling up to shm.c's unlock handling. Remove the recently added barrier, not needed now we have spin_unlock() before the scan. Use get_file(), with subsequent fput(), to make sure we have a reference to mapping throughout scan_mapping_unevictable_pages(): that's something that was previously guaranteed by the shm_lock(). Remove shmctl's lru_add_drain_all(): we don't fault in pages at SHM_LOCK time, and we lazily discover them to be Unevictable later, so it serves no purpose for SHM_LOCK; and serves no purpose for SHM_UNLOCK, since pages still on pagevec are not marked Unevictable. The original code avoided redundant rescans by checking VM_LOCKED flag at its level: now avoid them by checking shp's SHM_LOCKED. The original code called scan_mapping_unevictable_pages() on a locked area at shm_destroy() time: perhaps we once had accounting cross-checks which required that, but not now, so skip the overhead and just let inode eviction deal with them. Put check_move_unevictable_page() and scan_mapping_unevictable_pages() under CONFIG_SHMEM (with stub for the TINY case when ramfs is used), more as comment than to save space; comment them used for SHM_UNLOCK. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Shaohua Li <shaohua.li@intel.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc/shm.c')
1 files changed, 22 insertions, 15 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index 02ecf2c078fc..854ab58e5f6e 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -870,9 +870,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
case SHM_LOCK:
- struct file *uninitialized_var(shm_file);
- lru_add_drain_all(); /* drain pagevecs to lru lists */
+ struct file *shm_file;
shp = shm_lock_check(ns, shmid);
if (IS_ERR(shp)) {
@@ -895,22 +893,31 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
err = security_shm_shmctl(shp, cmd);
if (err)
goto out_unlock;
- if(cmd==SHM_LOCK) {
+ shm_file = shp->shm_file;
+ if (is_file_hugepages(shm_file))
+ goto out_unlock;
+ if (cmd == SHM_LOCK) {
struct user_struct *user = current_user();
- if (!is_file_hugepages(shp->shm_file)) {
- err = shmem_lock(shp->shm_file, 1, user);
- if (!err && !(shp->shm_perm.mode & SHM_LOCKED)){
- shp->shm_perm.mode |= SHM_LOCKED;
- shp->mlock_user = user;
- }
+ err = shmem_lock(shm_file, 1, user);
+ if (!err && !(shp->shm_perm.mode & SHM_LOCKED)) {
+ shp->shm_perm.mode |= SHM_LOCKED;
+ shp->mlock_user = user;
- } else if (!is_file_hugepages(shp->shm_file)) {
- shmem_lock(shp->shm_file, 0, shp->mlock_user);
- shp->shm_perm.mode &= ~SHM_LOCKED;
- shp->mlock_user = NULL;
+ goto out_unlock;
+ /* SHM_UNLOCK */
+ if (!(shp->shm_perm.mode & SHM_LOCKED))
+ goto out_unlock;
+ shmem_lock(shm_file, 0, shp->mlock_user);
+ shp->shm_perm.mode &= ~SHM_LOCKED;
+ shp->mlock_user = NULL;
+ get_file(shm_file);
+ scan_mapping_unevictable_pages(shm_file->f_mapping);
+ fput(shm_file);
goto out;
case IPC_RMID: