Re: [PATCH v3 4/4] drm/xe: Bump prefetch BO LRU for already-valid ranges

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

On Tue, Sep 22, 2026 at 10:08:04AM +0530, Himal Prasad Ghimiray wrote:
> A valid prefetch range skips migration and binding, so nothing refreshes
> its backing BOs on the LRU. Add xe_svm_range_prefetch_lru_bump(), which
> re-faults with no_dma_map and bumps each backing BO, and call it on the
> valid path.
> 
> v2
> - Make function failsafe (Matt/Sashiko AI comment)
> - Add stub for function
> 
> Suggested-by: Matthew Brost <matthew.brost@intel.com>

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

> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c | 34 ++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_svm.h | 11 +++++++++++
>  drivers/gpu/drm/xe/xe_vm.c  |  5 +++++
>  3 files changed, 50 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 018836ecbb06..10f81086f183 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -1655,6 +1655,40 @@ void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation)
>  #endif
>  }
>  
> +/**
> + * xe_svm_range_prefetch_lru_bump() - Bump the TTM LRU for an already-valid range
> + * @vm: Pointer to the struct xe_vm
> + * @vma: Pointer to the VMA covering the range
> + * @range: Pointer to the xe SVM range structure
> + * @dpagemap: Target pagemap of the prefetch, or %NULL for system memory
> + *
> + * A valid range skips migration and binding, so nothing else refreshes its
> + * backing BOs on the LRU. Re-fault the CPU pages without touching the DMA
> + * mappings (@no_dma_map) and move each backing BO to the LRU tail.
> + *
> + * Prefetching is a best-effort optimization, so any failure is ignored; a
> + * later fault will refault the range.
> + */
> +void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
> +				    struct xe_svm_range *range,
> +				    struct drm_pagemap *dpagemap)
> +{
> +	struct drm_gpusvm_ctx ctx = {
> +		.read_only = xe_vma_read_only(vma),
> +		.device_private_page_owner =
> +			xe_svm_private_page_owner(vm, !dpagemap),
> +		.no_dma_map = 1,
> +		.devmem_fn = xe_svm_devmem_lru_bump,
> +	};
> +
> +	guard(mutex)(&range->lock);
> +
> +	if (xe_svm_range_is_removed(range))
> +		return;
> +
> +	xe_svm_range_get_pages(vm, range, &ctx);
> +}
> +
>  /**
>   * xe_svm_ranges_zap_ptes_in_range - clear ptes of svm ranges in input range
>   * @vm: Pointer to the xe_vm structure
> diff --git a/drivers/gpu/drm/xe/xe_svm.h b/drivers/gpu/drm/xe/xe_svm.h
> index 585ad64b672b..ffc1cc808102 100644
> --- a/drivers/gpu/drm/xe/xe_svm.h
> +++ b/drivers/gpu/drm/xe/xe_svm.h
> @@ -130,6 +130,10 @@ int xe_svm_range_get_pages(struct xe_vm *vm, struct xe_svm_range *range,
>  
>  void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation);
>  
> +void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
> +				    struct xe_svm_range *range,
> +				    struct drm_pagemap *dpagemap);
> +
>  bool xe_svm_range_needs_migrate_to_vram(struct xe_svm_range *range, struct xe_vma *vma,
>  					const struct drm_pagemap *dpagemap);
>  
> @@ -363,6 +367,13 @@ void xe_svm_devmem_lru_bump(struct drm_pagemap_devmem *devmem_allocation)
>  {
>  }
>  
> +static inline
> +void xe_svm_range_prefetch_lru_bump(struct xe_vm *vm, struct xe_vma *vma,
> +				    struct xe_svm_range *range,
> +				    struct drm_pagemap *dpagemap)
> +{
> +}
> +
>  static inline struct xe_svm_range *to_xe_range(struct drm_gpusvm_range *r)
>  {
>  	return NULL;
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 0fdc740f1a41..3d5c5f3788bd 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2584,6 +2584,11 @@ vm_bind_ioctl_ops_create(struct xe_vm *vm, struct xe_vma_ops *vops,
>  						  dpagemap, &valid_pages)) {
>  				xe_svm_range_debug(svm_range, "PREFETCH - RANGE IS VALID");
>  				xe_assert(vm->xe, valid_pages);
> +
> +				if (dpagemap)
> +					xe_svm_range_prefetch_lru_bump(vm, vma, svm_range,
> +								       dpagemap);
> +
>  				need_put = true;
>  				goto check_next_range;
>  			}
> -- 
> 2.43.0
>