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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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