[PATCH] ext4: use percpu counter for extent cache count

[Eric Sandeen <sandeen@redhat.com>]

Use a percpu counter rather than atomic types for shrinker accounting.
There's no need for ultimate accuracy in the shrinker, so this
should come a little more cheaply.  The percpu struct is somewhat
large, but there was a big gap before the cache-aligned
s_es_lru_lock anyway, and it fits nicely in there.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 96c1093..4a01ba3 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1268,7 +1268,6 @@ struct ext4_sb_info {
 	atomic_t s_mb_preallocated;
 	atomic_t s_mb_discarded;
 	atomic_t s_lock_busy;
-	atomic_t s_extent_cache_cnt;
 
 	/* locality groups */
 	struct ext4_locality_group __percpu *s_locality_groups;
@@ -1310,6 +1309,7 @@ struct ext4_sb_info {
 	/* Reclaim extents from extent status tree */
 	struct shrinker s_es_shrinker;
 	struct list_head s_es_lru;
+	struct percpu_counter s_extent_cache_cnt;
 	spinlock_t s_es_lru_lock ____cacheline_aligned_in_smp;
 };
 
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 27fcdd2..95796a1 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -305,7 +305,7 @@ ext4_es_alloc_extent(struct inode *inode, ext4_lblk_t lblk, ext4_lblk_t len,
 	 */
 	if (!ext4_es_is_delayed(es)) {
 		EXT4_I(inode)->i_es_lru_nr++;
-		atomic_inc(&EXT4_SB(inode->i_sb)->s_extent_cache_cnt);
+		percpu_counter_inc(&EXT4_SB(inode->i_sb)->s_extent_cache_cnt);
 	}
 
 	return es;
@@ -317,7 +317,7 @@ static void ext4_es_free_extent(struct inode *inode, struct extent_status *es)
 	if (!ext4_es_is_delayed(es)) {
 		BUG_ON(EXT4_I(inode)->i_es_lru_nr == 0);
 		EXT4_I(inode)->i_es_lru_nr--;
-		atomic_dec(&EXT4_SB(inode->i_sb)->s_extent_cache_cnt);
+		percpu_counter_dec(&EXT4_SB(inode->i_sb)->s_extent_cache_cnt);
 	}
 
 	kmem_cache_free(ext4_es_cachep, es);
@@ -678,7 +678,7 @@ static int ext4_es_shrink(struct shrinker *shrink, struct shrink_control *sc)
 	int nr_to_scan = sc->nr_to_scan;
 	int ret, nr_shrunk = 0;
 
-	ret = atomic_read(&sbi->s_extent_cache_cnt);
+	ret = percpu_counter_read_positive(&sbi->s_extent_cache_cnt);
 	trace_ext4_es_shrink_enter(sbi->s_sb, nr_to_scan, ret);
 
 	if (!nr_to_scan)
@@ -711,7 +711,7 @@ static int ext4_es_shrink(struct shrinker *shrink, struct shrink_control *sc)
 	list_splice_tail(&scanned, &sbi->s_es_lru);
 	spin_unlock(&sbi->s_es_lru_lock);
 
-	ret = atomic_read(&sbi->s_extent_cache_cnt);
+	ret = percpu_counter_read_positive(&sbi->s_extent_cache_cnt);
 	trace_ext4_es_shrink_exit(sbi->s_sb, nr_shrunk, ret);
 	return ret;
 }