ext4: use percpu counter for extent cache count

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>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 10 insertions, 5 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 96c10934bb96..4a01ba315262 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 27fcdd2b2607..95796a1b7522 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;
 }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 373d46cd5d3f..1ae5860b30a3 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -783,6 +783,7 @@ static void ext4_put_super(struct super_block *sb)
         percpu_counter_destroy(&sbi->s_freeinodes_counter);
         percpu_counter_destroy(&sbi->s_dirs_counter);
         percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
+        percpu_counter_destroy(&sbi->s_extent_cache_cnt);
         brelse(sbi->s_sbh);
 #ifdef CONFIG_QUOTA
         for (i = 0; i < MAXQUOTAS; i++)
@@ -3688,6 +3689,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         if (!err) {
                 err = percpu_counter_init(&sbi->s_dirtyclusters_counter, 0);
         }
+        if (!err) {
+                err = percpu_counter_init(&sbi->s_extent_cache_cnt, 0);
+        }
         if (err) {
                 ext4_msg(sb, KERN_ERR, "insufficient memory");
                 goto failed_mount3;
@@ -3993,6 +3997,7 @@ failed_mount3:
         percpu_counter_destroy(&sbi->s_freeinodes_counter);
         percpu_counter_destroy(&sbi->s_dirs_counter);
         percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
+        percpu_counter_destroy(&sbi->s_extent_cache_cnt);
         if (sbi->s_mmp_tsk)
                 kthread_stop(sbi->s_mmp_tsk);
 failed_mount2: