Re: [PATCH v2 2/2] block: share request flush fields with elevator_private

Vivek Goyal
2011-02-02T21:53:10Z

On Tue, Feb 01, 2011 at 05:46:13PM -0500, Mike Snitzer wrote:
> 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'.
>

Looks good to me.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Vivek

> 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