Re: [PATCH v8 4/6] drm/ttm: Add a shrinker helper and export the LRU walker for driver use

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

On Fri, Aug 16, 2024 at 03:37:15PM +0200, Thomas Hellström wrote:
> Following the design direction communicated here:
> 
> https://lore.kernel.org/linux-mm/b7491378-defd-4f1c-31e2-29e4c77e2d67@amd.com/T/#ma918844aa8a6efe8768fdcda0c6590d5c93850c9
> 
> Export the LRU walker for driver shrinker use and add a bo
> shrinker helper for initial use by the xe driver.
> 
> v8:
> - Split out from another patch.
> - Use a struct for bool arguments to increase readability (Matt Brost).
> - Unmap user-space cpu-mappings before shrinking pages.
> - Explain non-fatal error codes (Matt Brost)
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

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

> ---
>  drivers/gpu/drm/ttm/ttm_bo_util.c | 65 +++++++++++++++++++++++++++++++
>  include/drm/ttm/ttm_bo.h          | 17 ++++++++
>  2 files changed, 82 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 3c07f4712d5c..3490e3347de9 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -919,3 +919,68 @@ s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
>  
>  	return progress;
>  }
> +EXPORT_SYMBOL(ttm_lru_walk_for_evict);
> +
> +/**
> + * ttm_bo_try_shrink - LRU walk helper to shrink a ttm buffer object.
> + * @walk: The struct xe_ttm_lru_walk that describes the walk.
> + * @bo: The buffer object.
> + * @flags: Flags governing the shrinking behaviour.
> + *
> + * The function uses the ttm_tt_back_up functionality to back up or
> + * purge a struct ttm_tt. If the bo is not in system, it's first
> + * moved there, unless @flags.allow_move is false.
> + *
> + * Return: The number of pages shrunken or purged, or
> + * negative error code on failure.
> + */
> +long ttm_bo_try_shrink(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo,
> +		       const struct ttm_bo_shrink_flags flags)
> +{
> +	static const struct ttm_place sys_placement_flags = {
> +		.fpfn = 0,
> +		.lpfn = 0,
> +		.mem_type = TTM_PL_SYSTEM,
> +		.flags = 0,
> +	};
> +	static struct ttm_placement sys_placement = {
> +		.num_placement = 1,
> +		.placement = &sys_placement_flags,
> +	};
> +	struct ttm_operation_ctx *ctx = walk->ctx;
> +	struct ttm_tt *tt = bo->ttm;
> +	long lret;
> +
> +	dma_resv_assert_held(bo->base.resv);
> +
> +	if (!tt || !ttm_tt_is_populated(tt))
> +		return 0;
> +
> +	if (flags.allow_move && bo->resource->mem_type != TTM_PL_SYSTEM) {
> +		int ret = ttm_bo_validate(bo, &sys_placement, ctx);
> +
> +		/* Consider -ENOMEM and -ENOSPC non-fatal. */
> +		if (ret) {
> +			if (ret == -ENOMEM || ret == -ENOSPC)
> +				ret = -EBUSY;
> +			return ret;
> +		}
> +	}
> +
> +	ttm_bo_unmap_virtual(bo);
> +	lret = ttm_bo_wait_ctx(bo, ctx);
> +	if (lret < 0) {
> +		if (lret == -ERESTARTSYS)
> +			return lret;
> +		return 0;
> +	}
> +
> +	lret = ttm_tt_backup(bo->bdev, tt, (struct ttm_backup_flags)
> +			     {.purge = flags.purge,
> +			      .writeback = flags.writeback});
> +	if (lret < 0 && lret != -EINTR)
> +		return 0;
> +
> +	return lret;
> +}
> +EXPORT_SYMBOL(ttm_bo_try_shrink);
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index d1a732d56259..479ada85cea1 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -229,6 +229,23 @@ struct ttm_lru_walk {
>  s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
>  			   struct ttm_resource_manager *man, s64 target);
>  
> +/**
> + * struct ttm_bo_shrink_flags - flags to govern the bo shrinking behaviour
> + * @purge: Purge the content rather than backing it up.
> + * @writeback: Attempt to immediately write content to swap space.
> + * @allow_move: Allow moving to system before shrinking. This is typically
> + * not desired for zombie- or ghost objects (with zombie object meaning
> + * objects with a zero gem object refcount)
> + */
> +struct ttm_bo_shrink_flags {
> +	u32 purge : 1;
> +	u32 writeback : 1;
> +	u32 allow_move : 1;
> +};
> +
> +long ttm_bo_try_shrink(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo,
> +		       const struct ttm_bo_shrink_flags flags);
> +
>  /**
>   * ttm_bo_get - reference a struct ttm_buffer_object
>   *
> -- 
> 2.44.0
>