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block: skip elevator data initialization for flush requests 

Skip elevator initialization for flush requests by passing priv=0 to
blk_alloc_request() in get_request().  As such elv_set_request() is
never called for flush requests.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Mike Snitzer 2011-02-11 11:05:46 +01:00 committed by Jens Axboe
parent ae1b153962
commit 9d5a4e946c
1 changed files with 25 additions and 4 deletions
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23
block/blk-core.c
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@ -737,6 +737,25 @@ static void freed_request(struct request_queue *q, int sync, int priv)
__freed_request(q, sync ^ 1);
}
/*
* Determine if elevator data should be initialized when allocating the
* request associated with @bio.
*/
static bool blk_rq_should_init_elevator(struct bio *bio)
{
if (!bio)
return true;
/*
* Flush requests do not use the elevator so skip initialization.
* This allows a request to share the flush and elevator data.
*/
if (bio->bi_rw & (REQ_FLUSH | REQ_FUA))
return false;
return true;
}
/*
* Get a free request, queue_lock must be held.
* Returns NULL on failure, with queue_lock held.
@ -749,7 +768,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
struct request_list *rl = &q->rq;
struct io_context *ioc = NULL;
const bool is_sync = rw_is_sync(rw_flags) != 0;
int may_queue, priv;
int may_queue, priv = 0;
may_queue = elv_may_queue(q, rw_flags);
if (may_queue == ELV_MQUEUE_NO)
@ -793,9 +812,11 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
rl->count[is_sync]++;
rl->starved[is_sync] = 0;
if (blk_rq_should_init_elevator(bio)) {
priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
if (priv)
rl->elvpriv++;
}
if (blk_queue_io_stat(q))
rw_flags |= REQ_IO_STAT;