[PATCH] cfq-iosched: tighten allow merge criteria
The logic in cfq_allow_merge() wasn't clear enough - basically allow
merging for the same queues only. Do a fast check for 'rq and bio both
sync/async' before doing the cfqq hash lookup.
This is verified to work with the fixed elv_try_merge() from commit
bb4067e34159648d394943d5e2a011f838bff22f.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9fc5eaf..4b4217d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -577,25 +577,20 @@
pid_t key;
/*
- * If bio is async or a write, always allow merge
+ * Disallow merge, if bio and rq aren't both sync or async
*/
- if (!bio_sync(bio) || rw == WRITE)
- return 1;
-
- /*
- * bio is sync. if request is not, disallow.
- */
- if (!rq_is_sync(rq))
+ if (!!bio_sync(bio) != !!rq_is_sync(rq))
return 0;
/*
- * Ok, both bio and request are sync. Allow merge if they are
- * from the same queue.
+ * Lookup the cfqq that this bio will be queued with. Allow
+ * merge only if rq is queued there.
*/
- key = cfq_queue_pid(current, rw, 1);
+ key = cfq_queue_pid(current, rw, bio_sync(bio));
cfqq = cfq_find_cfq_hash(cfqd, key, current->ioprio);
- if (cfqq != RQ_CFQQ(rq))
- return 0;
+
+ if (cfqq == RQ_CFQQ(rq))
+ return 1;
return 1;
}