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Subject: Re: [PATCH 3/3] xen/swiotlb: remember having called
 xen_create_contiguous_region()
To:     Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org
Cc:     konrad.wilk@oracle.com, sstabellini@kernel.org
References: <20190423105457.17502-1-jgross@suse.com>
 <20190423105457.17502-4-jgross@suse.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Message-ID: <b4917f80-a8ce-d38f-5c59-ef266669cea3@oracle.com>
Date:   Tue, 23 Apr 2019 10:31:49 -0400
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On 4/23/19 6:54 AM, Juergen Gross wrote:
> Instead of always calling xen_destroy_contiguous_region() in case the
> memory is DMA-able for the used device, do so only in case it has been
> made DMA-able via xen_create_contiguous_region() before.
>
> This will avoid a lot of xen_destroy_contiguous_region() calls for
> 64-bit capable devices.
>
> As the memory in question is owned by swiotlb-xen the PG_owner_priv_1
> flag of the first allocated page can be used for remembering.

I think a new enum in pageflags would be useful, and be consistent with
other flag uses.

-boris


>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  drivers/xen/swiotlb-xen.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 43b6e65ae256..a72f181d8e20 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -321,6 +321,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
>  			xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
>  			return NULL;
>  		}
> +		SetPageOwnerPriv1(virt_to_page(ret));
>  	}
>  	memset(ret, 0, size);
>  	return ret;
> @@ -344,9 +345,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>  	/* Convert the size to actually allocated. */
>  	size = 1UL << (order + XEN_PAGE_SHIFT);
>  
> -	if ((dev_addr + size - 1 <= dma_mask) &&
> -	    !WARN_ON(range_straddles_page_boundary(phys, size)))
> -		xen_destroy_contiguous_region(phys, order);
> +	if (PageOwnerPriv1(virt_to_page(vaddr))) {
> +		if (!WARN_ON(range_straddles_page_boundary(phys, size)))
> +			xen_destroy_contiguous_region(phys, order);
> +		ClearPageOwnerPriv1(virt_to_page(vaddr));
> +	}
>  
>  	xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
>  }