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/include/linux/quota.h b/include/linux/quota.h
index eccc1cb..0741239 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -298,12 +298,13 @@ struct dquot {
struct list_head dq_free; /* Free list element */
struct list_head dq_dirty; /* List of dirty dquots */
struct mutex dq_lock; /* dquot IO lock */
+ spinlock_t dq_dqb_lock; /* Lock protecting dq_dqb changes */
atomic_t dq_count; /* Use count */
struct super_block *dq_sb; /* superblock this applies to */
struct kqid dq_id; /* ID this applies to (uid, gid, projid) */
loff_t dq_off; /* Offset of dquot on disk */
unsigned long dq_flags; /* See DQ_* */
- struct mem_dqblk dq_dqb; /* Diskquota usage */
+ struct mem_dqblk dq_dqb; /* Diskquota usage [dq_dqb_lock] */
};
/* Operations which must be implemented by each quota format */