On 08/07/13 14:03, Roger Pau Monne wrote:
> Prevent blkfront from hoarding all grants by adding a minimum number
> of grants that must be free at all times. We still need a way to free
> unused grants in blkfront, but this patch will mitigate the problem
> in the meantime.
I think this could end up with the a frontend being able to get no
grants because some other frontend always grabs the free grants first.
Particularly as the free grant callbacks are done in the wrong order.
David
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -101,6 +101,12 @@ MODULE_PARM_DESC(max, "Maximum amount of segments in
> indirect requests (default
> #define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)
>
> /*
> + * Make sure there are at least MIN_FREE_GRANTS at all times, preventing
> + * blkfront from hoarding all grants
> + */
> +#define MIN_FREE_GRANTS 512
> +
> +/*
> * We have one of these per vbd, whether ide, scsi or 'other'. They
> * hang in private_data off the gendisk structure. We may end up
> * putting all kinds of interesting stuff here :-)
> @@ -412,13 +418,13 @@ static int blkif_queue_request(struct request *req)
> if (info->persistent_gnts_c < max_grefs) {
> new_persistent_gnts = 1;
> if (gnttab_alloc_grant_references(
> - max_grefs - info->persistent_gnts_c,
> + max_grefs - info->persistent_gnts_c + MIN_FREE_GRANTS,
> &gref_head) < 0) {
> gnttab_request_free_callback(
> &info->callback,
> blkif_restart_queue_callback,
> info,
> - max_grefs);
> + max_grefs + MIN_FREE_GRANTS);
> return 1;
> }
> } else
--
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