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authorJens Axboe <jaxboe@fusionio.com>2011-03-21 10:14:27 +0100
committerJens Axboe <jaxboe@fusionio.com>2011-03-21 10:14:27 +0100
commit5e84ea3a9c662dc2d7a48703a4468fad954a3b7f (patch)
tree3fa0fb26a7c8a970213584104cc2498ef46d60a3
parent4345caba340f051e10847924fc078ae18ed6695c (diff)
block: attempt to merge with existing requests on plug flush
One of the disadvantages of on-stack plugging is that we potentially lose out on merging since all pending IO isn't always visible to everybody. When we flush the on-stack plugs, right now we don't do any checks to see if potential merge candidates could be utilized. Correct this by adding a new insert variant, ELEVATOR_INSERT_SORT_MERGE. It works just ELEVATOR_INSERT_SORT, but first checks whether we can merge with an existing request before doing the insertion (if we fail merging). This fixes a regression with multiple processes issuing IO that can be merged. Thanks to Shaohua Li <shaohua.li@intel.com> for testing and fixing an accounting bug. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
-rw-r--r--block/blk-core.c2
-rw-r--r--block/blk-merge.c6
-rw-r--r--block/blk.h2
-rw-r--r--block/elevator.c52
-rw-r--r--include/linux/elevator.h1
5 files changed, 59 insertions, 4 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index e1fcf7a24668..525693237a4a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2685,7 +2685,7 @@ static void flush_plug_list(struct blk_plug *plug)
/*
* rq is already accounted, so use raw insert
*/
- __elv_add_request(q, rq, ELEVATOR_INSERT_SORT);
+ __elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);
}
if (q) {
diff --git a/block/blk-merge.c b/block/blk-merge.c
index ea85e20d5e94..cfcc37cb222b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -465,3 +465,9 @@ int attempt_front_merge(struct request_queue *q, struct request *rq)
return 0;
}
+
+int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
+ struct request *next)
+{
+ return attempt_merge(q, rq, next);
+}
diff --git a/block/blk.h b/block/blk.h
index 49d21af81d07..c8db371a921d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -103,6 +103,8 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
struct bio *bio);
int attempt_back_merge(struct request_queue *q, struct request *rq);
int attempt_front_merge(struct request_queue *q, struct request *rq);
+int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
+ struct request *next);
void blk_recalc_rq_segments(struct request *rq);
void blk_rq_set_mixed_merge(struct request *rq);
diff --git a/block/elevator.c b/block/elevator.c
index 542ce826b401..c387d3168734 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -521,6 +521,40 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
return ELEVATOR_NO_MERGE;
}
+/*
+ * Attempt to do an insertion back merge. Only check for the case where
+ * we can append 'rq' to an existing request, so we can throw 'rq' away
+ * afterwards.
+ *
+ * Returns true if we merged, false otherwise
+ */
+static bool elv_attempt_insert_merge(struct request_queue *q,
+ struct request *rq)
+{
+ struct request *__rq;
+
+ if (blk_queue_nomerges(q))
+ return false;
+
+ /*
+ * First try one-hit cache.
+ */
+ if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
+ return true;
+
+ if (blk_queue_noxmerges(q))
+ return false;
+
+ /*
+ * See if our hash lookup can find a potential backmerge.
+ */
+ __rq = elv_rqhash_find(q, blk_rq_pos(rq));
+ if (__rq && blk_attempt_req_merge(q, __rq, rq))
+ return true;
+
+ return false;
+}
+
void elv_merged_request(struct request_queue *q, struct request *rq, int type)
{
struct elevator_queue *e = q->elevator;
@@ -538,14 +572,18 @@ void elv_merge_requests(struct request_queue *q, struct request *rq,
struct request *next)
{
struct elevator_queue *e = q->elevator;
+ const int next_sorted = next->cmd_flags & REQ_SORTED;
- if (e->ops->elevator_merge_req_fn)
+ if (next_sorted && e->ops->elevator_merge_req_fn)
e->ops->elevator_merge_req_fn(q, rq, next);
elv_rqhash_reposition(q, rq);
- elv_rqhash_del(q, next);
- q->nr_sorted--;
+ if (next_sorted) {
+ elv_rqhash_del(q, next);
+ q->nr_sorted--;
+ }
+
q->last_merge = rq;
}
@@ -647,6 +685,14 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
__blk_run_queue(q, false);
break;
+ case ELEVATOR_INSERT_SORT_MERGE:
+ /*
+ * If we succeed in merging this request with one in the
+ * queue already, we are done - rq has now been freed,
+ * so no need to do anything further.
+ */
+ if (elv_attempt_insert_merge(q, rq))
+ break;
case ELEVATOR_INSERT_SORT:
BUG_ON(rq->cmd_type != REQ_TYPE_FS &&
!(rq->cmd_flags & REQ_DISCARD));
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index ec6f72b84477..d93efcc44570 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -166,6 +166,7 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
#define ELEVATOR_INSERT_SORT 3
#define ELEVATOR_INSERT_REQUEUE 4
#define ELEVATOR_INSERT_FLUSH 5
+#define ELEVATOR_INSERT_SORT_MERGE 6
/*
* return values from elevator_may_queue_fn