quota: Reduce contention on dq_data_lock

dq_data_lock is currently used to protect all modifications of quota
accounting information, consistency of quota accounting on the inode,
and dquot pointers from inode. As a result contention on the lock can be
pretty heavy.

Reduce the contention on the lock by protecting quota accounting
information by a new dquot->dq_dqb_lock and consistency of quota
accounting with inode usage by inode->i_lock.

This change reduces time to create 500000 files on ext4 on ramdisk by 50
different processes in separate directories by 6% when user quota is
turned on. When those 50 processes belong to 50 different users, the
improvement is about 9%.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/quota/quota_tree.c b/fs/quota/quota_tree.c
index 54f85eb2609c..bb3f59bcfcf5 100644
--- a/fs/quota/quota_tree.c
+++ b/fs/quota/quota_tree.c
@@ -389,9 +389,9 @@ int qtree_write_dquot(struct qtree_mem_dqinfo *info, struct dquot *dquot)
 			return ret;
 		}
 	}
-	spin_lock(&dq_data_lock);
+	spin_lock(&dquot->dq_dqb_lock);
 	info->dqi_ops->mem2disk_dqblk(ddquot, dquot);
-	spin_unlock(&dq_data_lock);
+	spin_unlock(&dquot->dq_dqb_lock);
 	ret = sb->s_op->quota_write(sb, type, ddquot, info->dqi_entry_size,
 				    dquot->dq_off);
 	if (ret != info->dqi_entry_size) {
@@ -649,14 +649,14 @@ int qtree_read_dquot(struct qtree_mem_dqinfo *info, struct dquot *dquot)
 		kfree(ddquot);
 		goto out;
 	}
-	spin_lock(&dq_data_lock);
+	spin_lock(&dquot->dq_dqb_lock);
 	info->dqi_ops->disk2mem_dqblk(dquot, ddquot);
 	if (!dquot->dq_dqb.dqb_bhardlimit &&
 	    !dquot->dq_dqb.dqb_bsoftlimit &&
 	    !dquot->dq_dqb.dqb_ihardlimit &&
 	    !dquot->dq_dqb.dqb_isoftlimit)
 		set_bit(DQ_FAKE_B, &dquot->dq_flags);
-	spin_unlock(&dq_data_lock);
+	spin_unlock(&dquot->dq_dqb_lock);
 	kfree(ddquot);
 out:
 	dqstats_inc(DQST_READS);