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, 2 insertions, 2 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 16a877a0f309..67ce21224dab 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5194,7 +5194,7 @@ static int ext4_statfs_project(struct super_block *sb,
         dquot = dqget(sb, qid);
         if (IS_ERR(dquot))
                 return PTR_ERR(dquot);
-        spin_lock(&dq_data_lock);
+        spin_lock(&dquot->dq_dqb_lock);
 
         limit = (dquot->dq_dqb.dqb_bsoftlimit ?
                  dquot->dq_dqb.dqb_bsoftlimit :
@@ -5217,7 +5217,7 @@ static int ext4_statfs_project(struct super_block *sb,
                          (buf->f_files - dquot->dq_dqb.dqb_curinodes) : 0;
         }
 
-        spin_unlock(&dq_data_lock);
+        spin_unlock(&dquot->dq_dqb_lock);
         dqput(dquot);
         return 0;
 }