Re: [PATCH 11/11] IB/srp: Prevent mapping failures

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Fri, Apr 22, 2016 at 02:16:31PM -0700, Bart Van Assche wrote:
> If both max_sectors and the queue_depth are high enough it can
> happen that the MR pool is depleted temporarily. This causes
> the SRP initiator to report mapping failures. Although the SRP
> initiator recovers from such mapping failures, prevent that
> this can happen by limiting max_sectors.
> 
> Reported-by: Laurence Oberman <loberman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>
> Cc: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
> Cc: Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
> ---
>  drivers/infiniband/ulp/srp/ib_srp.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
> index a173ec4..ebd4d90 100644
> --- a/drivers/infiniband/ulp/srp/ib_srp.c
> +++ b/drivers/infiniband/ulp/srp/ib_srp.c
> @@ -3172,6 +3172,7 @@ static ssize_t srp_create_target(struct device *dev,
>  	struct srp_device *srp_dev = host->srp_dev;
>  	struct ib_device *ibdev = srp_dev->dev;
>  	int ret, node_idx, node, cpu, i;
> +	unsigned int max_max_sectors;
>  	bool multich = false;
>  
>  	target_host = scsi_host_alloc(&srp_template,
> @@ -3228,6 +3229,25 @@ static ssize_t srp_create_target(struct device *dev,
>  		target->sg_tablesize = target->cmd_sg_cnt;
>  	}
>  
> +	if (srp_dev->use_fast_reg || srp_dev->use_fmr) {
> +		/*
> +		 * FR and FMR can only map one HCA page per entry. If the
> +		 * start address is not aligned on a HCA page boundary two
> +		 * entries will be used for the head and the tail although
> +		 * these two entries combined contain at most one HCA page of
> +		 * data. Hence the "- 1" in the calculation below.
> +		 */
> +		max_max_sectors = (srp_dev->max_pages_per_mr - 1) <<
> +				  (ilog2(srp_dev->mr_page_size) - 9);

From my understanding, srp_dev->max_pages_per_mr can be equal to 1, in
case device will advertise it.

Is this understanding correct?
Will the code work in such case?

> +		if (target->scsi_host->max_sectors > max_max_sectors) {
> +			shost_printk(KERN_WARNING, target->scsi_host,
> +				     PFX "Reducing max_sectors from %d to %d\n",
> +				     target->scsi_host->max_sectors,
> +				     max_max_sectors);
> +			target->scsi_host->max_sectors = max_max_sectors;
> +		}
> +	}
> +
>  	target_host->sg_tablesize = target->sg_tablesize;
>  	target->mr_pool_size = target->scsi_host->can_queue;
>  	target->indirect_size = target->sg_tablesize *
> -- 
> 2.8.1
> 
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