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authorRoger Pau Monne <roger.pau@citrix.com>2013-08-12 12:53:43 +0200
committerJens Axboe <axboe@kernel.dk>2013-11-08 09:10:27 -0700
commitc47206e25f28232ff979994c32758c82841d81cd (patch)
tree5b3a5b0830778f0bffaa97eee715f7a99ac3f01b /drivers/block/xen-blkfront.c
parentfbe363c476afe8ec992d3baf682670a4bd1b6ce6 (diff)
downloadop-kernel-dev-c47206e25f28232ff979994c32758c82841d81cd.zip
op-kernel-dev-c47206e25f28232ff979994c32758c82841d81cd.tar.gz
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>
Diffstat (limited to 'drivers/block/xen-blkfront.c')
-rw-r--r--drivers/block/xen-blkfront.c11
1 files changed, 7 insertions, 4 deletions
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 429d526..5b8a154 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -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) {
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