vfs: revert per-cpu nr_unused counters for dentry and inodes

The nr_unused counters count the number of objects on an LRU, and as such they
are synchronized with LRU object insertion and removal and scanning, and
protected under the LRU lock.

Making it per-cpu does not actually get any concurrency improvements because of
this lock, and summing the counter is much slower, and
incrementing/decrementing it costs more code size and is slower too.

These counters should stay per-LRU, which currently means global.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 7 insertions, 10 deletions

diff --git a/fs/inode.c b/fs/inode.c
index ae2727a..efc4397 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -103,7 +103,6 @@ static DECLARE_RWSEM(iprune_sem);
 struct inodes_stat_t inodes_stat;
 
 static struct percpu_counter nr_inodes __cacheline_aligned_in_smp;
-static struct percpu_counter nr_inodes_unused __cacheline_aligned_in_smp;
 
 static struct kmem_cache *inode_cachep __read_mostly;
 
@@ -114,7 +113,7 @@ static inline int get_nr_inodes(void)
 
 static inline int get_nr_inodes_unused(void)
 {
-	return percpu_counter_sum_positive(&nr_inodes_unused);
+	return inodes_stat.nr_unused;
 }
 
 int get_nr_dirty_inodes(void)
@@ -132,7 +131,6 @@ int proc_nr_inodes(ctl_table *table, int write,
 		   void __user *buffer, size_t *lenp, loff_t *ppos)
 {
 	inodes_stat.nr_inodes = get_nr_inodes();
-	inodes_stat.nr_unused = get_nr_inodes_unused();
 	return proc_dointvec(table, write, buffer, lenp, ppos);
 }
 #endif
@@ -335,7 +333,7 @@ static void inode_lru_list_add(struct inode *inode)
 {
 	if (list_empty(&inode->i_lru)) {
 		list_add(&inode->i_lru, &inode_lru);
-		percpu_counter_inc(&nr_inodes_unused);
+		inodes_stat.nr_unused++;
 	}
 }
 
@@ -343,7 +341,7 @@ static void inode_lru_list_del(struct inode *inode)
 {
 	if (!list_empty(&inode->i_lru)) {
 		list_del_init(&inode->i_lru);
-		percpu_counter_dec(&nr_inodes_unused);
+		inodes_stat.nr_unused--;
 	}
 }
 
@@ -513,7 +511,7 @@ void evict_inodes(struct super_block *sb)
 		list_move(&inode->i_lru, &dispose);
 		list_del_init(&inode->i_wb_list);
 		if (!(inode->i_state & (I_DIRTY | I_SYNC)))
-			percpu_counter_dec(&nr_inodes_unused);
+			inodes_stat.nr_unused--;
 	}
 	spin_unlock(&inode_lock);
 
@@ -554,7 +552,7 @@ int invalidate_inodes(struct super_block *sb)
 		list_move(&inode->i_lru, &dispose);
 		list_del_init(&inode->i_wb_list);
 		if (!(inode->i_state & (I_DIRTY | I_SYNC)))
-			percpu_counter_dec(&nr_inodes_unused);
+			inodes_stat.nr_unused--;
 	}
 	spin_unlock(&inode_lock);
 
@@ -616,7 +614,7 @@ static void prune_icache(int nr_to_scan)
 		if (atomic_read(&inode->i_count) ||
 		    (inode->i_state & ~I_REFERENCED)) {
 			list_del_init(&inode->i_lru);
-			percpu_counter_dec(&nr_inodes_unused);
+			inodes_stat.nr_unused--;
 			continue;
 		}
 
@@ -650,7 +648,7 @@ static void prune_icache(int nr_to_scan)
 		 */
 		list_move(&inode->i_lru, &freeable);
 		list_del_init(&inode->i_wb_list);
-		percpu_counter_dec(&nr_inodes_unused);
+		inodes_stat.nr_unused--;
 	}
 	if (current_is_kswapd())
 		__count_vm_events(KSWAPD_INODESTEAL, reap);
@@ -1649,7 +1647,6 @@ void __init inode_init(void)
 					 init_once);
 	register_shrinker(&icache_shrinker);
 	percpu_counter_init(&nr_inodes, 0);
-	percpu_counter_init(&nr_inodes_unused, 0);
 
 	/* Hash may have been set up in inode_init_early */
 	if (!hashdist)