Commit 719d3402 authored by Jens Axboe's avatar Jens Axboe Committed by Linus Torvalds

[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
bb4067e3.
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent c2fda5fe
......@@ -577,25 +577,20 @@ static int cfq_allow_merge(request_queue_t *q, struct request *rq,
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;
}
......
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