[PATCH] nvme: use __GFP_NOWARN for iod allocation

[hch@infradead.org (Christoph Hellwig)]

I guess we can live with it for now with a big comment

>  	ctrl->cntlid = le16_to_cpup(&id->cntlid);
>  	if (id->mdts)
>  		max_hw_sectors = 1 << (id->mdts + page_shift - 9);
> -	else
> +	else if (ctrl->ops->flags & NVME_F_FABRICS)
>  		max_hw_sectors = UINT_MAX;
> +	else
> +		max_hw_sectors = NVME_MAX_KB_SZ << 1;

Can this I think is better done by setting ctrl->max_hw_sectors
in the PCIe driver (similar to what the other drivers already do)
and then rely on the min_not_zero below to factor in MDTS.

> +/*
> + * These can be higher, but we need to ensure that any command doesn't
> + * require an sg allocation that needs more than a page of data.
> + */
> +#define NVME_MAX_KB_SZ	4096

I think this should move the pci.c

> +#define NVME_MAX_SEGS	127

And this could use a good explanation.  Especially as I think
that we shouldn't apply the limit for fabrics.  So instead we
might just add a new ctrl->max_segments field, which PCI sets,
and which then is min() with the otherwise calculated value.