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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: 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>
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1 changed files with 7 additions and 4 deletions
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@ -400,10 +400,13 @@ static int blkif_queue_request(struct request *req)
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if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
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return 1;
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max_grefs = info->max_indirect_segments ?
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info->max_indirect_segments +
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INDIRECT_GREFS(info->max_indirect_segments) :
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BLKIF_MAX_SEGMENTS_PER_REQUEST;
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max_grefs = req->nr_phys_segments;
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if (max_grefs > BLKIF_MAX_SEGMENTS_PER_REQUEST)
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/*
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* If we are using indirect segments we need to account
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* for the indirect grefs used in the request.
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*/
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max_grefs += INDIRECT_GREFS(req->nr_phys_segments);
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/* Check if we have enough grants to allocate a requests */
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if (info->persistent_gnts_c < max_grefs) {
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