vmscan: use atomic-long for shrinker batching

Use atomic-long operations instead of looping around cmpxchg().

[akpm@linux-foundation.org: massage atomic.h inclusions]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 10 insertions, 12 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 019dc558df1..e0bc4ffb8e7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -393,8 +393,8 @@ struct inodes_stat_t {
 #include <linux/semaphore.h>
 #include <linux/fiemap.h>
 #include <linux/rculist_bl.h>
-#include <linux/shrinker.h>
 #include <linux/atomic.h>
+#include <linux/shrinker.h>
 
 #include <asm/byteorder.h>
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3dc3a8c2c48..4baadd18f4a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -10,6 +10,7 @@
 #include <linux/mmzone.h>
 #include <linux/rbtree.h>
 #include <linux/prio_tree.h>
+#include <linux/atomic.h>
 #include <linux/debug_locks.h>
 #include <linux/mm_types.h>
 #include <linux/range.h>
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index a83833a1f7a..07ceb97d53f 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -35,7 +35,7 @@ struct shrinker {
 
         /* These are for internal use */
         struct list_head list;
-        long nr;        /* objs pending delete */
+        atomic_long_t nr_in_batch; /* objs pending delete */
 };
 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
 extern void register_shrinker(struct shrinker *);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f5255442ae2..f54a05b7a61 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -183,7 +183,7 @@ static unsigned long zone_nr_lru_pages(struct zone *zone,
  */
 void register_shrinker(struct shrinker *shrinker)
 {
-        shrinker->nr = 0;
+        atomic_long_set(&shrinker->nr_in_batch, 0);
         down_write(&shrinker_rwsem);
         list_add_tail(&shrinker->list, &shrinker_list);
         up_write(&shrinker_rwsem);
@@ -264,9 +264,7 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                  * and zero it so that other concurrent shrinker invocations
                  * don't also do this scanning work.
                  */
-                do {
-                        nr = shrinker->nr;
-                } while (cmpxchg(&shrinker->nr, nr, 0) != nr);
+                nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
 
                 total_scan = nr;
                 delta = (4 * nr_pages_scanned) / shrinker->seeks;
@@ -328,12 +326,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                  * manner that handles concurrent updates. If we exhausted the
                  * scan, there is no need to do an update.
                  */
-                do {
-                        nr = shrinker->nr;
-                        new_nr = total_scan + nr;
-                        if (total_scan <= 0)
-                                break;
-                } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
+                if (total_scan > 0)
+                        new_nr = atomic_long_add_return(total_scan,
+                                        &shrinker->nr_in_batch);
+                else
+                        new_nr = atomic_long_read(&shrinker->nr_in_batch);
 
                 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
         }