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xen-blkfront: improve aproximation of required grants per request

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Improve the calculation of required grants to process a request by
using nr_phys_segments instead of always assuming a request is going
to use all posible segments.

nr_phys_segments contains the number of scatter-gather DMA addr+len
pairs, which is basically what we put at every granted page.
for_each_sg iterates over the DMA addr+len pairs and uses a grant
page for each of them.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Roger Pau Monne 2013-08-12 12:53:43 +02:00 committed by Jens Axboe
parent fbe363c476
commit c47206e25f
1 changed files with 7 additions and 4 deletions
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11
drivers/block/xen-blkfront.c
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@ -400,10 +400,13 @@ static int blkif_queue_request(struct request *req)
if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
return 1;
max_grefs = info->max_indirect_segments ?
info->max_indirect_segments +
INDIRECT_GREFS(info->max_indirect_segments) :
BLKIF_MAX_SEGMENTS_PER_REQUEST;
max_grefs = req->nr_phys_segments;
if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
/*
* If we are using indirect segments we need to account
* for the indirect grefs used in the request.
*/
max_grefs += INDIRECT_GREFS(req->nr_phys_segments);
/* Check if we have enough grants to allocate a requests */
if (info->persistent_gnts_c < max_grefs) {