Re: [PATCH v4 8/8] drm/xe/bo: Add purgeable shrinker state helpers

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

On Tue, Jan 20, 2026 at 11:38:54AM +0530, Arvind Yadav wrote:
> Encapsulate TTM purgeable flag updates and shrinker page accounting
> into helper functions. This prevents desynchronization between the
> TTM tt->purgeable flag and the shrinker's page bucket counters.
> 
> Without these helpers, direct manipulation of xe_ttm_tt->purgeable
> risks forgetting to update the corresponding shrinker counters,
> leading to incorrect memory pressure calculations.
> 
> Add xe_bo_set_purgeable_shrinker() and xe_bo_clear_purgeable_shrinker()
> which atomically update both the TTM flag and transfer pages between
> the shrinkable and purgeable buckets.
> 
> v4:
>   - @madv_purgeable atomic_t → u32 change across all relevant patches. (Matt)
> 
> Cc: Matthew Brost <matthew.brost@intel.com>

I think this patch is right but best to double check with Thomas as he
wrote the shrinker logic and is the expert here.

Matt

> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_bo.c         | 60 ++++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_bo.h         |  3 ++
>  drivers/gpu/drm/xe/xe_vm_madvise.c | 13 +++++--
>  3 files changed, 73 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index cc547915161d..2b1448ea3aed 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -836,6 +836,66 @@ static int xe_bo_move_notify(struct xe_bo *bo,
>  	return 0;
>  }
>  
> +/**
> + * xe_bo_set_purgeable_shrinker() - Mark BO purgeable and update shrinker
> + * @bo: Buffer object
> + *
> + * Transfers pages from shrinkable to purgeable bucket. Shrinker can now
> + * discard pages immediately without swapping. Caller holds BO lock.
> + */
> +void xe_bo_set_purgeable_shrinker(struct xe_bo *bo)
> +{
> +	struct ttm_buffer_object *ttm_bo = &bo->ttm;
> +	struct ttm_tt *tt = ttm_bo->ttm;
> +	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> +	struct xe_ttm_tt *xe_tt;
> +
> +	xe_bo_assert_held(bo);
> +
> +	if (!tt || !ttm_tt_is_populated(tt))
> +		return;
> +
> +	xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
> +
> +	if (!xe_tt->purgeable) {
> +		xe_tt->purgeable = true;
> +		/* Transfer pages from shrinkable to purgeable count */
> +		xe_shrinker_mod_pages(xe->mem.shrinker,
> +				      -(long)tt->num_pages,
> +				      tt->num_pages);
> +	}
> +}
> +
> +/**
> + * xe_bo_clear_purgeable_shrinker() - Mark BO non-purgeable and update shrinker
> + * @bo: Buffer object
> + *
> + * Transfers pages from purgeable to shrinkable bucket. Shrinker must now
> + * swap pages instead of discarding. Caller holds BO lock.
> + */
> +void xe_bo_clear_purgeable_shrinker(struct xe_bo *bo)
> +{
> +	struct ttm_buffer_object *ttm_bo = &bo->ttm;
> +	struct ttm_tt *tt = ttm_bo->ttm;
> +	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> +	struct xe_ttm_tt *xe_tt;
> +
> +	xe_bo_assert_held(bo);
> +
> +	if (!tt || !ttm_tt_is_populated(tt))
> +		return;
> +
> +	xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
> +
> +	if (xe_tt->purgeable) {
> +		xe_tt->purgeable = false;
> +		/* Transfer pages from purgeable to shrinkable count */
> +		xe_shrinker_mod_pages(xe->mem.shrinker,
> +				      tt->num_pages,
> +				      -(long)tt->num_pages);
> +	}
> +}
> +
>  /**
>   * xe_ttm_bo_purge() - Purge buffer object backing store
>   * @ttm_bo: The TTM buffer object to purge
> diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
> index 00e93b3065c9..681495e905af 100644
> --- a/drivers/gpu/drm/xe/xe_bo.h
> +++ b/drivers/gpu/drm/xe/xe_bo.h
> @@ -270,6 +270,9 @@ static inline bool xe_bo_madv_is_dontneed(struct xe_bo *bo)
>  	return bo->madv_purgeable == XE_MADV_PURGEABLE_DONTNEED;
>  }
>  
> +void xe_bo_set_purgeable_shrinker(struct xe_bo *bo);
> +void xe_bo_clear_purgeable_shrinker(struct xe_bo *bo);
> +
>  static inline void xe_bo_unpin_map_no_vm(struct xe_bo *bo)
>  {
>  	if (likely(bo)) {
> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
> index 5808fef89777..0fb07a1ed3ae 100644
> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> @@ -274,12 +274,16 @@ void xe_bo_recheck_purgeable_on_vma_unbind(struct xe_bo *bo)
>  
>  	if (xe_bo_all_vmas_dontneed(bo)) {
>  		/* All VMAs are DONTNEED - mark BO purgeable */
> -		if (bo->madv_purgeable != XE_MADV_PURGEABLE_DONTNEED)
> +		if (bo->madv_purgeable != XE_MADV_PURGEABLE_DONTNEED) {
>  			bo->madv_purgeable = XE_MADV_PURGEABLE_DONTNEED;
> +			xe_bo_set_purgeable_shrinker(bo);
> +		}
>  	} else {
>  		/* At least one VMA is WILLNEED - BO must not be purgeable */
> -		if (bo->madv_purgeable != XE_MADV_PURGEABLE_WILLNEED)
> +		if (bo->madv_purgeable != XE_MADV_PURGEABLE_WILLNEED) {
>  			bo->madv_purgeable = XE_MADV_PURGEABLE_WILLNEED;
> +			xe_bo_clear_purgeable_shrinker(bo);
> +		}
>  	}
>  }
>  
> @@ -325,13 +329,16 @@ static bool xe_vm_madvise_purgeable_bo(struct xe_device *xe, struct xe_vm *vm,
>  
>  			/* Mark VMA WILLNEED - BO becomes non-purgeable immediately */
>  			bo->madv_purgeable = XE_MADV_PURGEABLE_WILLNEED;
> +			xe_bo_clear_purgeable_shrinker(bo);
>  			break;
>  		case DRM_XE_VMA_PURGEABLE_STATE_DONTNEED:
>  			vmas[i]->purgeable_state = XE_MADV_PURGEABLE_DONTNEED;
>  
>  			/* Mark BO purgeable only if all VMAs are DONTNEED */
> -			if (xe_bo_all_vmas_dontneed(bo))
> +			if (xe_bo_all_vmas_dontneed(bo)) {
>  				bo->madv_purgeable = XE_MADV_PURGEABLE_DONTNEED;
> +				xe_bo_set_purgeable_shrinker(bo);
> +			}
>  			break;
>  		default:
>  			drm_warn(&vm->xe->drm, "Invalid madvice value = %d\n",
> -- 
> 2.43.0
>