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[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
bb4067e341.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Jens Axboe 2006-12-22 09:38:53 +01:00 committed by Linus Torvalds
parent c2fda5fed8
commit 719d34027e
1 changed files with 8 additions and 13 deletions
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21
block/cfq-iosched.c
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@ -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;
}