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


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