Re: [PATCH v2 6/6] drm/xe/svm: Migrate folios when possible

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Jul 25, 2025 at 05:39:30PM +0200, Francois Dugast wrote:
> The DMA mapping can now correspond to a folio (order > 0), so move the
> iterator by the number of pages in the folio in order to migrate all
> pages at once. This will improve efficiency compared to migrating pages
> one by one.
> 
> For this to work, the BOs must be contiguous in memory.
> 

I'd mention since SVM BOs are a max of 2M and it is very unlikely
forcing to continuous has any negative affects (e.g., extra eviction),
it greatly simplifies the code, and 2M contiguous memory will enable 2M
device pages which is huge perf win.

We might need a small adjustment to populate_devmem_pfn to communicate
contigous memory was found to drm_pagemap too as our driver can easily
allocate contiguous memory, but we shouldn't assume other drivers can
do so. This can be done in follow up which adds the 2M device page
support.

> Signed-off-by: Francois Dugast <francois.dugast@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_bo.c  | 2 ++
>  drivers/gpu/drm/xe/xe_svm.c | 5 +++++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index ffca1cea5585..59994a978a8c 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -200,6 +200,8 @@ static bool force_contiguous(u32 bo_flags)
>  	else if (bo_flags & XE_BO_FLAG_PINNED &&
>  		 !(bo_flags & XE_BO_FLAG_PINNED_LATE_RESTORE))
>  		return true; /* needs vmap */
> +	else if (bo_flags & XE_BO_FLAG_CPU_ADDR_MIRROR)
> +		return true;
>  
>  	/*
>  	 * For eviction / restore on suspend / resume objects pinned in VRAM
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 1d097e76aabc..2759db5f7407 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -382,6 +382,11 @@ static int xe_svm_copy(struct page **pages,
>  				pos = i;
>  			}
>  
> +			if (pagemap_addr[i].order) {
> +				i += NR_PAGES(pagemap_addr[i].order);

I think this needs to be NR_PAGES(pagemap_addr[i].order) - 1, right?

> +				last = (i + 1) == npages;

Then set the chunk here too?

> +			}
> +
>  			match = vram_addr + PAGE_SIZE * (i - pos) == __vram_addr;

I think the match can be dropped actually and just assume it is true if
we are allocating continuous memory now.

Matt

>  		}
>  
> -- 
> 2.43.0
>