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Subject[PATCH 07/13] Use atomic-long operations instead of looping around cmpxchg().
Date
From: Konstantin Khlebnikov <khlebnikov@openvz.org>

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
---
include/linux/fs.h | 2 +-
include/linux/shrinker.h | 2 +-
mm/vmscan.c | 17 +++++++----------
3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 958c025..2651059 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -394,8 +394,8 @@ 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/shrinker.h b/include/linux/shrinker.h
index ab6c572..02b5b6b 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -43,7 +43,7 @@ struct shrinker {

/* These are for internal use */
struct list_head list;
- long nr; /* objs pending delete */
+ atomic_long_t nr_pending; /* objs pending delete */
};

#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e32ce2d..534ed34 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -184,7 +184,7 @@ static unsigned long zone_nr_lru_pages(struct zone *zone,
*/
void register_shrinker(struct shrinker *shrinker)
{
- shrinker->nr = 0;
+ atomic_long_set(&shrinker->nr_pending, 0);
down_write(&shrinker_rwsem);
list_add_tail(&shrinker->list, &shrinker_list);
up_write(&shrinker_rwsem);
@@ -252,9 +252,7 @@ unsigned long shrink_slab(struct shrink_control *sc,
* 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_pending, 0);

total_scan = nr;
max_pass = shrinker->count_objects(shrinker, sc);
@@ -318,12 +316,11 @@ unsigned long shrink_slab(struct shrink_control *sc,
* 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_pending);
+ else
+ new_nr = atomic_long_read(&shrinker->nr_pending);

trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr);
}
--
1.7.5.4


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