vmscan: use atomic-long for shrinker batching
Konstantin Khlebnikov [Thu, 8 Dec 2011 22:33:54 +0000 (14:33 -0800)]
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>

include/linux/fs.h
include/linux/mm.h
include/linux/shrinker.h
mm/vmscan.c

index 019dc55..e0bc4ff 100644 (file)
@@ -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>
 
index 3dc3a8c..4baadd1 100644 (file)
@@ -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>
index a83833a..07ceb97 100644 (file)
@@ -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 *);
index f525544..f54a05b 100644 (file)
@@ -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);
        }