Re: [PATCH V2 2/2] nvme-pci: use max of PRP or SGL for iod size

[Christoph Hellwig <hch@lst.de>]

On Thu, Jul 09, 2020 at 04:40:25PM -0700, Chaitanya Kulkarni wrote:
> >From the initial implementation of NVMe SGL kernel support
> commit a7a7cbe353a5 ("nvme-pci: add SGL support") with addition of the
> commit 943e942e6266 ("nvme-pci: limit max IO size and segments to avoid
> high order allocations") now there is only caller left for
> nvme_pci_iod_alloc_size() which statically passes true for last
> parameter that calculates allocation size based on SGL since we need
> size of biggest command supported for mempool allocation.
> 
> This patch modifies the helper functions nvme_pci_iod_alloc_size() such
> that it is now uses maximum of PRP and SGL size for iod allocation size
> calculation.
> 
> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
> ---
>  drivers/nvme/host/pci.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 68f7c090cf51..8b6792005360 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -363,14 +363,13 @@ static int nvme_pci_npages_sgl(unsigned int num_seg)
>  }
>  
>  static size_t nvme_pci_iod_alloc_size(struct nvme_dev *dev,
> -		unsigned int size, unsigned int nseg, bool use_sgl)
> +		unsigned int size, unsigned int nseg)
>  {
> -	size_t alloc_size;
> +	size_t npages_sgl = nvme_pci_npages_sgl(nseg);
> +	size_t npages = nvme_npages(size, dev);
> +	size_t alloc_size = sizeof(__le64 *);
>  
> -	if (use_sgl)
> -		alloc_size = sizeof(__le64 *) * nvme_pci_npages_sgl(nseg);
> -	else
> -		alloc_size = sizeof(__le64 *) * nvme_npages(size, dev);
> +	alloc_size *= max_t(size_t, npages_sgl, npages);
>  
>  	return alloc_size + sizeof(struct scatterlist) * nseg;
>  }
> @@ -2812,7 +2811,7 @@ static int nvme_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	 * command we support.
>  	 */
>  	alloc_size = nvme_pci_iod_alloc_size(dev, NVME_MAX_KB_SZ,
> -						NVME_MAX_SEGS, true);
> +						NVME_MAX_SEGS);

I think we can just remove the size and nseg arguments and hard code them
in the function itself.

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