aio: make the lookup_ioctx() lockless
The mm->ioctx_list is currently protected by a reader-writer lock,
so we always grab that lock on the read side for doing ioctx
lookups. As the workload is extremely reader biased, turn this into
an rcu hlist so we can make lookup_ioctx() lockless. Get rid of
the rwlock and use a spinlock for providing update side exclusion.
There's usually only 1 entry on this list, so it doesn't make sense
to look into fancier data structures.
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index ef3635b..0767827 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -263,7 +263,7 @@
/* lets check if we are allowed to replace the mm */
task_lock(tsk);
if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
- tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
+ tsk->mm != tsk->active_mm || !hlist_empty(&tsk->mm->ioctx_list)) {
task_unlock(tsk);
return -EINVAL;
}
@@ -279,7 +279,7 @@
/* Now lets check again if something happened */
task_lock(tsk);
if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
- tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
+ tsk->mm != tsk->active_mm || !hlist_empty(&tsk->mm->ioctx_list)) {
mmput(mm);
task_unlock(tsk);
return -EINVAL;