commit 1ea06bec78a128adc995ca32bd906a6c9bb9cf91
Author: Niu Yawei <yawei.niu@gmail.com>
Date:   Wed Jun 4 12:20:30 2014 +0800

    quota: avoid unnecessary dqget()/dqput() calls

    Avoid unnecessary dqget()/dqput() calls in __dquot_initialize(),
    that will introduce global lock contention otherwise.

    Signed-off-by: Lai Siyao <lai.siyao@intel.com>
    Signed-off-by: Niu Yawei <yawei.niu@intel.com>
    Signed-off-by: Jan Kara <jack@suse.cz>
Index: linux-2.6.32-431.5.1.el6/fs/quota/dquot.c
===================================================================
--- linux-2.6.32-431.5.1.el6.orig/fs/quota/dquot.c
+++ linux-2.6.32-431.5.1.el6/fs/quota/dquot.c
@@ -1230,7 +1230,7 @@ static int info_bdq_free(struct dquot *d
 int dquot_initialize(struct inode *inode, int type)
 {
 	unsigned int id = 0;
-	int cnt, ret = 0;
+	int cnt, ret = 0, init_needed = 0;
 	struct dquot *got[MAXQUOTAS] = { NULL, NULL };
 	struct super_block *sb = inode->i_sb;
 	qsize_t rsv;
@@ -1244,6 +1244,15 @@ int dquot_initialize(struct inode *inode
 	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
 		if (type != -1 && cnt != type)
 			continue;
+		/*
+		 * The i_dquot should have been initialized in most cases,
+		 * we check it without locking here to avoid unnecessary
+		 * dqget()/dqput() calls.
+		 */
+		if (inode->i_dquot[cnt])
+			continue;
+		init_needed = 1;
+
 		switch (cnt) {
 		case USRQUOTA:
 			id = inode->i_uid;
@@ -1255,6 +1264,10 @@ int dquot_initialize(struct inode *inode
 		got[cnt] = dqget(sb, id, cnt);
 	}
 
+	/* All required i_dquot has been initialized */
+	if (!init_needed)
+		return 0;
+
 	spin_lock(&inode->i_lock);
 	if (IS_NOQUOTA(inode))
 		goto out_err;
@@ -1264,6 +1277,9 @@ int dquot_initialize(struct inode *inode
 		/* Avoid races with quotaoff() */
 		if (!sb_has_quota_active(sb, cnt))
 			continue;
+		/* We could race with quotaon or dqget() could have failed */
+		if (!got[cnt])
+			continue;
 		if (!inode->i_dquot[cnt]) {
 			inode->i_dquot[cnt] = got[cnt];
 			got[cnt] = NULL;