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Commit c47206e2 authored by Roger Pau Monne's avatar Roger Pau Monne Committed by Jens Axboe
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xen-blkfront: improve aproximation of required grants per request 



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: default avatarRoger Pau Monné <roger.pau@citrix.com>
Reviewed-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent fbe363c4

drivers/block/xen-blkfront.c

+7 −4
Original line number Diff line number Diff line
@@ -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) {