Re: [PATCH 2/2] nvme-pci: use dma_alloc_noncontigous if possible

[Keith Busch <kbusch@kernel.org>]

On Mon, Dec 02, 2024 at 09:05:41PM +0200, Leon Romanovsky wrote:
> I see at least two possible solutions, add GFP_NOWARN in nvme_alloc_host_mem_single()
> or the following patch:
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 4c644bb7f069..baed4059d8a5 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -2172,7 +2172,8 @@ static int nvme_alloc_host_mem_multi(struct nvme_dev *dev, u64 preferred,
> 
>  static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>  {
> -       u64 min_chunk = min_t(u64, preferred, PAGE_SIZE * MAX_ORDER_NR_PAGES);
> +       u64 max_chunk = PAGE_SIZE * MAX_ORDER_NR_PAGES;
> +       u64 min_chunk = min_t(u64, preferred, max_chunk);
>         u64 hmminds = max_t(u32, dev->ctrl.hmminds * 4096, PAGE_SIZE * 2);
>         u64 chunk_size;
> 
> @@ -2180,7 +2181,7 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
>          * If there is an IOMMU that can merge pages, try a virtually
>          * non-contiguous allocation for a single segment first.
>          */
> -       if (!(PAGE_SIZE & dma_get_merge_boundary(dev->dev))) {
> +       if (!(PAGE_SIZE & dma_get_merge_boundary(dev->dev)) && preferred < max_chunk) {
>                 if (!nvme_alloc_host_mem_single(dev, preferred))
>                         return 0;
>         }
> (END)
> 
> What is the preferred way to overcome the warning?

I think your max_chunk check suggestion looks pretty good.