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>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 16a877a..67ce212 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5194,7 +5194,7 @@
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 @@
(buf->f_files - dquot->dq_dqb.dqb_curinodes) : 0;
}
- spin_unlock(&dq_data_lock);
+ spin_unlock(&dquot->dq_dqb_lock);
dqput(dquot);
return 0;
}