Re: [PATCH v4 20/22] drm/xe: Use drm_gpusvm_scan_mm()

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

On Thu, Dec 11, 2025 at 05:59:07PM +0100, Thomas Hellström wrote:
> Use drm_gpusvm_scan_mm() to avoid unnecessarily calling into
> drm_pagemap_populate_mm();
> 
> v3:
> - New patch.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 2fa73143fcd5..22281d69e26a 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -1625,11 +1625,23 @@ struct drm_pagemap *xe_vma_resolve_pagemap(struct xe_vma *vma, struct xe_tile *t
>  int xe_svm_alloc_vram(struct xe_svm_range *range, const struct drm_gpusvm_ctx *ctx,
>  		      struct drm_pagemap *dpagemap)
>  {
> -	struct xe_device *xe = range_to_vm(&range->base)->xe;
> +	struct xe_vm *vm = range_to_vm(&range->base);
> +	enum drm_gpusvm_scan_result migration_state;
> +	struct xe_device *xe = vm->xe;
>  
>  	xe_assert(range_to_vm(&range->base)->xe, range->base.pages.flags.migrate_devmem);
>  	range_debug(range, "ALLOCATE VRAM");
>  
> +	migration_state = drm_gpusvm_scan_mm(&range->base,
> +					     xe_svm_private_page_owner(vm, false),
> +					     dpagemap->pagemap);
> +
> +	if (migration_state == DRM_GPUSVM_SCAN_EQUAL) {
> +		if (IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM))
> +			drm_dbg(dpagemap->drm, "Already migrated!\n");
> +		return 0;

LGTM, but I suggest adding something like CONFIG_DRM_XE_DEBUG_VM to the
SVM code in a follow-up. We get spammed a ton just running
xe_exec_system_allocator, with a reasonable DRM printk debug value.
IMO, it’s best to hide most of the debug in this function behind a
Kconfig. CONFIG_DRM_XE_DEBUG_VM would also select the SVM level debug.

Anyways:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> +	}
> +
>  	if (IS_ENABLED(CONFIG_DRM_XE_DEBUG_VM))
>  		drm_dbg(&xe->drm, "Request migration to device memory on \"%s\".\n",
>  			dpagemap->drm->unique);
> -- 
> 2.51.1
>