Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=da775265021b61d5eb81df155e36cb0810f6df53
Commit: da775265021b61d5eb81df155e36cb0810f6df53
Parent: 8e5cfc45e7527eb5c8a9a22d56a7b9227e7c0913
Author: Jens Axboe <[EMAIL PROTECTED]>
AuthorDate: Wed Dec 20 11:04:12 2006 +0100
Committer: Jens Axboe <[EMAIL PROTECTED]>
CommitDate: Wed Dec 20 11:04:12 2006 +0100
[PATCH] cfq-iosched: don't allow sync merges across queues
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 <[EMAIL PROTECTED]>
---
block/cfq-iosched.c | 33 +++++++++++++++++++++++++++++++++
block/elevator.c | 26 ++++++++++++++++++++++----
include/linux/elevator.h | 3 +++
3 files changed, 58 insertions(+), 4 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 533a293..9fc5eaf 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -568,6 +568,38 @@ cfq_merged_requests(request_queue_t *q, struct request *rq,
cfq_remove_request(next);
}
+static int cfq_allow_merge(request_queue_t *q, struct request *rq,
+ struct bio *bio)
+{
+ struct cfq_data *cfqd = q->elevator->elevator_data;
+ const int rw = bio_data_dir(bio);
+ struct cfq_queue *cfqq;
+ pid_t key;
+
+ /*
+ * If bio is async or a write, always allow merge
+ */
+ if (!bio_sync(bio) || rw == WRITE)
+ return 1;
+
+ /*
+ * bio is sync. if request is not, disallow.
+ */
+ if (!rq_is_sync(rq))
+ return 0;
+
+ /*
+ * Ok, both bio and request are sync. Allow merge if they are
+ * from the same queue.
+ */
+ key = cfq_queue_pid(current, rw, 1);
+ cfqq = cfq_find_cfq_hash(cfqd, key, current->ioprio);
+ if (cfqq != RQ_CFQQ(rq))
+ return 0;
+
+ return 1;
+}
+
static inline void
__cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
@@ -2125,6 +2157,7 @@ static struct elevator_type iosched_cfq = {
.elevator_merge_fn = cfq_merge,
.elevator_merged_fn = cfq_merged_request,
.elevator_merge_req_fn = cfq_merged_requests,
+ .elevator_allow_merge_fn = cfq_allow_merge,
.elevator_dispatch_fn = cfq_dispatch_requests,
.elevator_add_req_fn = cfq_insert_request,
.elevator_activate_req_fn = cfq_activate_request,
diff --git a/block/elevator.c b/block/elevator.c
index c0063f3..62c7a30 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -51,6 +51,21 @@ static const int elv_hash_shift = 6;
#define ELV_ON_HASH(rq) (!hlist_unhashed(&(rq)->hash))
/*
+ * Query io scheduler to see if the current process issuing bio may be
+ * merged with rq.
+ */
+static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
+{
+ request_queue_t *q = rq->q;
+ elevator_t *e = q->elevator;
+
+ if (e->ops->elevator_allow_merge_fn)
+ return e->ops->elevator_allow_merge_fn(q, rq, bio);
+
+ return 1;
+}
+
+/*
* can we safely merge with this request?
*/
inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
@@ -65,12 +80,15 @@ inline int elv_rq_merge_ok(struct request *rq, struct bio
*bio)
return 0;
/*
- * same device and no special stuff set, merge is ok
+ * must be same device and not a special request
*/
- if (rq->rq_disk == bio->bi_bdev->bd_disk && !rq->special)
- return 1;
+ if (rq->rq_disk != bio->bi_bdev->bd_disk || !rq->special)
+ return 0;
- return 0;
+ if (!elv_iosched_allow_merge(rq, bio))
+ return 0;
+
+ return 1;
}
EXPORT_SYMBOL(elv_rq_merge_ok);
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index a24931d..e88fcbc 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -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;
-
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