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/include/linux/aio.h b/include/linux/aio.h
index f6b8cf9..b16a957 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -5,6 +5,7 @@
#include <linux/workqueue.h>
#include <linux/aio_abi.h>
#include <linux/uio.h>
+#include <linux/rcupdate.h>
#include <asm/atomic.h>
@@ -183,7 +184,7 @@
/* This needs improving */
unsigned long user_id;
- struct kioctx *next;
+ struct hlist_node list;
wait_queue_head_t wait;
@@ -199,6 +200,8 @@
struct aio_ring_info ring_info;
struct delayed_work wq;
+
+ struct rcu_head rcu_head;
};
/* prototypes */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fe82547..9cfc9b6 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -232,8 +232,9 @@
struct core_state *core_state; /* coredumping support */
/* aio bits */
- rwlock_t ioctx_list_lock; /* aio lock */
- struct kioctx *ioctx_list;
+ spinlock_t ioctx_lock;
+ struct hlist_head ioctx_list;
+
#ifdef CONFIG_MM_OWNER
/*
* "owner" points to a task that is regarded as the canonical