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[PATCH] cfq-iosched: don't allow sync merges across queues

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Currently we allow any merge, even if the io originates from different
processes. This can cause really bad starvation and unfairness, if those
ios happen to be synchronous (reads or direct writes).

So add a allow_merge hook to the io scheduler ops, so an io scheduler can
help decide whether a bio/process combination may be merged with an
existing request.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2006-12-20 11:04:12 +01:00
commit da77526502
3 changed files with 58 additions and 4 deletions
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3
include/linux/elevator.h
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@ -12,6 +12,8 @@ typedef void (elevator_merge_req_fn) (request_queue_t *, struct request *, struc
typedef void (elevator_merged_fn) (request_queue_t *, struct request *, int);
typedef int (elevator_allow_merge_fn) (request_queue_t *, struct request *, struct bio *);
typedef int (elevator_dispatch_fn) (request_queue_t *, int);
typedef void (elevator_add_req_fn) (request_queue_t *, struct request *);
@ -33,6 +35,7 @@ struct elevator_ops
elevator_merge_fn *elevator_merge_fn;
elevator_merged_fn *elevator_merged_fn;
elevator_merge_req_fn *elevator_merge_req_fn;
elevator_allow_merge_fn *elevator_allow_merge_fn;
elevator_dispatch_fn *elevator_dispatch_fn;
elevator_add_req_fn *elevator_add_req_fn;