Re: [PATCH v11 6/8] drm/ttm: Add helpers for shrinking

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

On Wed, Oct 16, 2024 at 10:55:57AM +0200, Thomas Hellström wrote:
> Add a number of helpers for shrinking that access core TTM and
> core MM functionality in a way that make them unsuitable for
> driver open-coding.
> 
> v11:
> - New patch (split off from previous) and additional helpers.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

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

> ---
>  drivers/gpu/drm/ttm/ttm_backup_shmem.c | 23 +++++++
>  drivers/gpu/drm/ttm/ttm_bo_util.c      | 95 +++++++++++++++++++++++++-
>  include/drm/ttm/ttm_backup.h           | 20 +++---
>  include/drm/ttm/ttm_bo.h               | 21 ++++++
>  4 files changed, 149 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_backup_shmem.c b/drivers/gpu/drm/ttm/ttm_backup_shmem.c
> index cfe4140cc59d..4046d56dcc8d 100644
> --- a/drivers/gpu/drm/ttm/ttm_backup_shmem.c
> +++ b/drivers/gpu/drm/ttm/ttm_backup_shmem.c
> @@ -5,6 +5,7 @@
>  
>  #include <drm/ttm/ttm_backup.h>
>  #include <linux/page-flags.h>
> +#include <linux/swap.h>
>  
>  /**
>   * struct ttm_backup_shmem - A shmem based ttm_backup subclass.
> @@ -107,6 +108,28 @@ static const struct ttm_backup_ops ttm_backup_shmem_ops = {
>  	.fini = ttm_backup_shmem_fini,
>  };
>  
> +/**
> + * ttm_backup_shmem_bytes_avail() - Report the approximate number of bytes of backup space
> + * left for backup.
> + *
> + * This function is intended also for driver use to indicate whether a
> + * backup attempt is meaningful.
> + *
> + * Return: An approximate size of backup space available.
> + */
> +u64 ttm_backup_shmem_bytes_avail(void)
> +{
> +	/*
> +	 * The idea behind backing up to shmem is that shmem objects may
> +	 * eventually be swapped out. So no point swapping out if there
> +	 * is no or low swap-space available. But the accuracy of this
> +	 * number also depends on shmem actually swapping out backed-up
> +	 * shmem objects without too much buffering.
> +	 */
> +	return (u64)get_nr_swap_pages() << PAGE_SHIFT;
> +}
> +EXPORT_SYMBOL_GPL(ttm_backup_shmem_bytes_avail);
> +
>  /**
>   * ttm_backup_shmem_create() - Create a shmem-based struct backup.
>   * @size: The maximum size (in bytes) to back up.
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 0cac02a9764c..e6d88557f2c0 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -28,7 +28,7 @@
>  /*
>   * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
>   */
> -
> +#include <linux/swap.h>
>  #include <linux/vmalloc.h>
>  
>  #include <drm/ttm/ttm_bo.h>
> @@ -1052,3 +1052,96 @@ struct ttm_buffer_object *ttm_bo_lru_cursor_first(struct ttm_bo_lru_cursor *curs
>  	return bo ? bo : ttm_bo_lru_cursor_next(curs);
>  }
>  EXPORT_SYMBOL(ttm_bo_lru_cursor_first);
> +
> +/**
> + * ttm_bo_shrink() - Helper to shrink a ttm buffer object.
> + * @ctx: The struct ttm_operation_ctx used for the shrinking operation.
> + * @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.
> + *
> + * Return: The number of pages shrunken or purged, or
> + * negative error code on failure.
> + */
> +long ttm_bo_shrink(struct ttm_operation_ctx *ctx, 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_tt *tt = bo->ttm;
> +	long lret;
> +
> +	dma_resv_assert_held(bo->base.resv);
> +
> +	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)
> +		return lret;
> +
> +	lret = ttm_tt_backup(bo->bdev, tt, (struct ttm_backup_flags)
> +			     {.purge = flags.purge,
> +			      .writeback = flags.writeback});
> +
> +	if (lret < 0 && lret != -EINTR)
> +		return -EBUSY;
> +
> +	return lret;
> +}
> +EXPORT_SYMBOL(ttm_bo_shrink);
> +
> +/**
> + * ttm_bo_shrink_suitable() - Whether a bo is suitable for shinking
> + * @ctx: The struct ttm_operation_ctx governing the shrinking.
> + * @bo: The candidate for shrinking.
> + *
> + * Check whether the object, given the information available to TTM,
> + * is suitable for shinking, This function can and should be used
> + * before attempting to shrink an object.
> + *
> + * Return: true if suitable. false if not.
> + */
> +bool ttm_bo_shrink_suitable(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx)
> +{
> +	return bo->ttm && ttm_tt_is_populated(bo->ttm) && !bo->pin_count &&
> +		(!ctx->no_wait_gpu ||
> +		 dma_resv_test_signaled(bo->base.resv, DMA_RESV_USAGE_BOOKKEEP));
> +}
> +EXPORT_SYMBOL(ttm_bo_shrink_suitable);
> +
> +/**
> + * ttm_bo_shrink_avoid_wait() - Whether to avoid waiting for GPU
> + * during shrinking
> + *
> + * In some situations, like direct reclaim, waiting (in particular gpu waiting)
> + * should be avoided since it may stall a system that could otherwise make progress
> + * shrinking something else less time consuming.
> + *
> + * Return: true if gpu waiting should be avoided, false if not.
> + */
> +bool ttm_bo_shrink_avoid_wait(void)
> +{
> +	return !current_is_kswapd();
> +}
> +EXPORT_SYMBOL(ttm_bo_shrink_avoid_wait);
> diff --git a/include/drm/ttm/ttm_backup.h b/include/drm/ttm/ttm_backup.h
> index 5f8c7d3069ef..0d38dc1fd441 100644
> --- a/include/drm/ttm/ttm_backup.h
> +++ b/include/drm/ttm/ttm_backup.h
> @@ -110,6 +110,15 @@ struct ttm_backup_ops {
>  	 * After a call to @fini, it's illegal to use the @backup pointer.
>  	 */
>  	void (*fini)(struct ttm_backup *backup);
> +
> +	/**
> +	 * bytes_avail: Report the approximate number of bytes of backup space
> +	 * left for backup.
> +	 * @backup: Pointer to the struct backup queried.
> +	 *
> +	 * Return: An approximate size of backup space available.
> +	 */
> +	u64 (*bytes_avail)(struct ttm_backup *backup);
>  };
>  
>  /**
> @@ -123,15 +132,8 @@ struct ttm_backup {
>  	const struct ttm_backup_ops *ops;
>  };
>  
> -/**
> - * ttm_backup_shmem_create() - Create a shmem-based struct backup.
> - * @size: The maximum size (in bytes) to back up.
> - *
> - * Create a backup utilizing shmem objects.
> - *
> - * Return: A pointer to a struct ttm_backup on success,
> - * an error pointer on error.
> - */
>  struct ttm_backup *ttm_backup_shmem_create(loff_t size);
>  
> +u64 ttm_backup_shmem_bytes_avail(void);
> +
>  #endif
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index 91ecbb64f6c8..24d8769bcb37 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -225,6 +225,27 @@ 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_shrink(struct ttm_operation_ctx *ctx, struct ttm_buffer_object *bo,
> +		   const struct ttm_bo_shrink_flags flags);
> +
> +bool ttm_bo_shrink_suitable(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx);
> +
> +bool ttm_bo_shrink_avoid_wait(void);
> +
>  /**
>   * ttm_bo_get - reference a struct ttm_buffer_object
>   *
> -- 
> 2.46.0
>