quota: Make quota stat accounting lockless.

Quota stats is mostly writable data structure. Let's alloc percpu
bucket for each value.

NOTE: dqstats_read() function is racy against dqstats_{inc,dec}
and may return inconsistent value. But this is ok since absolute
accuracy is not required.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/quota/quota_tree.c b/fs/quota/quota_tree.c
index f81f4bc..5b7f741 100644
--- a/fs/quota/quota_tree.c
+++ b/fs/quota/quota_tree.c
@@ -384,7 +384,7 @@
 	} else {
 		ret = 0;
 	}
-	dqstats.writes++;
+	dqstats_inc(DQST_WRITES);
 	kfree(ddquot);
 
 	return ret;
@@ -634,7 +634,7 @@
 	spin_unlock(&dq_data_lock);
 	kfree(ddquot);
 out:
-	dqstats.reads++;
+	dqstats_inc(DQST_READS);
 	return ret;
 }
 EXPORT_SYMBOL(qtree_read_dquot);