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Subject[PATCH v2 2/2] block: share request flush fields with elevator_private
Date
Flush requests are never put on the IO scheduler.  Convert request
structure's elevator_private* into an array and have the flush fields
share a union with it.

Reclaim the space lost in 'struct request' by moving 'completion_data'
back in the union with 'rb_node'.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
block/cfq-iosched.c | 18 +++++++++---------
block/elevator.c | 2 +-
include/linux/blkdev.h | 23 ++++++++++++-----------
3 files changed, 22 insertions(+), 21 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 501ffdf..8692958 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -54,9 +54,9 @@ static const int cfq_hist_divisor = 4;
#define CFQQ_SEEKY(cfqq) (hweight32(cfqq->seek_history) > 32/8)

#define RQ_CIC(rq) \
- ((struct cfq_io_context *) (rq)->elevator_private)
-#define RQ_CFQQ(rq) (struct cfq_queue *) ((rq)->elevator_private2)
-#define RQ_CFQG(rq) (struct cfq_group *) ((rq)->elevator_private3)
+ ((struct cfq_io_context *) (rq)->elevator_private[0])
+#define RQ_CFQQ(rq) (struct cfq_queue *) ((rq)->elevator_private[1])
+#define RQ_CFQG(rq) (struct cfq_group *) ((rq)->elevator_private[2])

static struct kmem_cache *cfq_pool;
static struct kmem_cache *cfq_ioc_pool;
@@ -3609,12 +3609,12 @@ static void cfq_put_request(struct request *rq)

put_io_context(RQ_CIC(rq)->ioc);

- rq->elevator_private = NULL;
- rq->elevator_private2 = NULL;
+ rq->elevator_private[0] = NULL;
+ rq->elevator_private[1] = NULL;

/* Put down rq reference on cfqg */
cfq_put_cfqg(RQ_CFQG(rq));
- rq->elevator_private3 = NULL;
+ rq->elevator_private[2] = NULL;

cfq_put_queue(cfqq);
}
@@ -3702,9 +3702,9 @@ new_queue:

cfqq->allocated[rw]++;
cfqq->ref++;
- rq->elevator_private = cic;
- rq->elevator_private2 = cfqq;
- rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
+ rq->elevator_private[0] = cic;
+ rq->elevator_private[1] = cfqq;
+ rq->elevator_private[2] = cfq_ref_get_cfqg(cfqq->cfqg);

spin_unlock_irqrestore(q->queue_lock, flags);

diff --git a/block/elevator.c b/block/elevator.c
index 270e097..f98e92e 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -764,7 +764,7 @@ int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
if (e->ops->elevator_set_req_fn)
return e->ops->elevator_set_req_fn(q, rq, gfp_mask);

- rq->elevator_private = NULL;
+ rq->elevator_private[0] = NULL;
return 0;
}

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8a082a5..e3ee74f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -99,25 +99,26 @@ struct request {
/*
* The rb_node is only used inside the io scheduler, requests
* are pruned when moved to the dispatch queue. So let the
- * flush fields share space with the rb_node.
+ * completion_data share space with the rb_node.
*/
union {
struct rb_node rb_node; /* sort/lookup */
- struct {
- unsigned int seq;
- struct list_head list;
- } flush;
+ void *completion_data;
};

- void *completion_data;
-
/*
* Three pointers are available for the IO schedulers, if they need
- * more they have to dynamically allocate it.
+ * more they have to dynamically allocate it. Flush requests are
+ * never put on the IO scheduler. So let the flush fields share
+ * space with the three elevator_private pointers.
*/
- void *elevator_private;
- void *elevator_private2;
- void *elevator_private3;
+ union {
+ void *elevator_private[3];
+ struct {
+ unsigned int seq;
+ struct list_head list;
+ } flush;
+ };

struct gendisk *rq_disk;
struct hd_struct *part;
--
1.7.3.4


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