Re: [PATCH 02/11] drm/ttm: fix busy memory to fail other user v8

[Daniel Vetter <daniel-/w4YWyX8dFk@public.gmane.org>]

On Tue, May 14, 2019 at 02:31:18PM +0200, Christian König wrote:
> From: Chunming Zhou <david1.zhou@amd.com>
> 
> heavy gpu job could occupy memory long time, which lead other user fail to get memory.
> 
> basically pick up Christian idea:
> 
> 1. Reserve the BO in DC using a ww_mutex ticket (trivial).
> 2. If we then run into this EBUSY condition in TTM check if the BO we need memory for (or rather the ww_mutex of its reservation object) has a ticket assigned.
> 3. If we have a ticket we grab a reference to the first BO on the LRU, drop the LRU lock and try to grab the reservation lock with the ticket.
> 4. If getting the reservation lock with the ticket succeeded we check if the BO is still the first one on the LRU in question (the BO could have moved).
> 5. If the BO is still the first one on the LRU in question we try to evict it as we would evict any other BO.
> 6. If any of the "If's" above fail we just back off and return -EBUSY.
> 
> v2: fix some minor check
> v3: address Christian v2 comments.
> v4: fix some missing
> v5: handle first_bo unlock and bo_get/put
> v6: abstract unified iterate function, and handle all possible usecase not only pinned bo.
> v7: pass request bo->resv to ttm_bo_evict_first
> v8 (chk): minimal coding style fix
> 
> Change-Id: I21423fb922f885465f13833c41df1e134364a8e7
> Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>

I think this closes a big gap between ttm and the bkl/struct_mutex
drivers - it's much easier to guarantee you can evict everything if
there's only a single lock :-)

Would be absolutely awesome if we could extract this as some kind of
building block, like we've done with lots of other ttm concepts already
(reservation_obj, fences, ...).

Just an aside really.
-Daniel

> ---
>  drivers/gpu/drm/ttm/ttm_bo.c | 113 +++++++++++++++++++++++++++++------
>  1 file changed, 96 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 2845fceb2fbd..e634d3a36923 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -766,11 +766,13 @@ EXPORT_SYMBOL(ttm_bo_eviction_valuable);
>   * b. Otherwise, trylock it.
>   */
>  static bool ttm_bo_evict_swapout_allowable(struct ttm_buffer_object *bo,
> -			struct ttm_operation_ctx *ctx, bool *locked)
> +			struct ttm_operation_ctx *ctx, bool *locked, bool *busy)
>  {
>  	bool ret = false;
>  
>  	*locked = false;
> +	if (busy)
> +		*busy = false;
>  	if (bo->resv == ctx->resv) {
>  		reservation_object_assert_held(bo->resv);
>  		if (ctx->flags & TTM_OPT_FLAG_ALLOW_RES_EVICT
> @@ -779,35 +781,46 @@ static bool ttm_bo_evict_swapout_allowable(struct ttm_buffer_object *bo,
>  	} else {
>  		*locked = reservation_object_trylock(bo->resv);
>  		ret = *locked;
> +		if (!ret && busy)
> +			*busy = true;
>  	}
>  
>  	return ret;
>  }
>  
> -static int ttm_mem_evict_first(struct ttm_bo_device *bdev,
> -			       uint32_t mem_type,
> -			       const struct ttm_place *place,
> -			       struct ttm_operation_ctx *ctx)
> +static struct ttm_buffer_object*
> +ttm_mem_find_evitable_bo(struct ttm_bo_device *bdev,
> +			 struct ttm_mem_type_manager *man,
> +			 const struct ttm_place *place,
> +			 struct ttm_operation_ctx *ctx,
> +			 struct ttm_buffer_object **first_bo,
> +			 bool *locked)
>  {
> -	struct ttm_bo_global *glob = bdev->glob;
> -	struct ttm_mem_type_manager *man = &bdev->man[mem_type];
>  	struct ttm_buffer_object *bo = NULL;
> -	bool locked = false;
> -	unsigned i;
> -	int ret;
> +	int i;
>  
> -	spin_lock(&glob->lru_lock);
> +	if (first_bo)
> +		*first_bo = NULL;
>  	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
>  		list_for_each_entry(bo, &man->lru[i], lru) {
> -			if (!ttm_bo_evict_swapout_allowable(bo, ctx, &locked))
> +			bool busy = false;
> +
> +			if (!ttm_bo_evict_swapout_allowable(bo, ctx, locked,
> +							    &busy)) {
> +				if (first_bo && !(*first_bo) && busy) {
> +					ttm_bo_get(bo);
> +					*first_bo = bo;
> +				}
>  				continue;
> +			}
>  
>  			if (place && !bdev->driver->eviction_valuable(bo,
>  								      place)) {
> -				if (locked)
> +				if (*locked)
>  					reservation_object_unlock(bo->resv);
>  				continue;
>  			}
> +
>  			break;
>  		}
>  
> @@ -818,9 +831,69 @@ static int ttm_mem_evict_first(struct ttm_bo_device *bdev,
>  		bo = NULL;
>  	}
>  
> +	return bo;
> +}
> +
> +static int ttm_mem_evict_first(struct ttm_bo_device *bdev,
> +			       uint32_t mem_type,
> +			       const struct ttm_place *place,
> +			       struct ttm_operation_ctx *ctx,
> +			       struct reservation_object *request_resv)
> +{
> +	struct ttm_bo_global *glob = bdev->glob;
> +	struct ttm_mem_type_manager *man = &bdev->man[mem_type];
> +	struct ttm_buffer_object *bo = NULL, *first_bo = NULL;
> +	bool locked = false;
> +	int ret;
> +
> +	spin_lock(&glob->lru_lock);
> +	bo = ttm_mem_find_evitable_bo(bdev, man, place, ctx, &first_bo,
> +				      &locked);
>  	if (!bo) {
> +		struct ww_acquire_ctx *acquire_ctx = request_resv->lock.ctx;
> +		struct ttm_operation_ctx busy_ctx;
> +
>  		spin_unlock(&glob->lru_lock);
> -		return -EBUSY;
> +		/* check if other user occupy memory too long time */
> +		if (!first_bo || !request_resv || !request_resv->lock.ctx) {
> +			if (first_bo)
> +				ttm_bo_put(first_bo);
> +			return -EBUSY;
> +		}
> +		if (first_bo->resv == request_resv) {
> +			ttm_bo_put(first_bo);
> +			return -EBUSY;
> +		}
> +		if (ctx->interruptible)
> +			ret = ww_mutex_lock_interruptible(&first_bo->resv->lock,
> +							  acquire_ctx);
> +		else
> +			ret = ww_mutex_lock(&first_bo->resv->lock,
> +					    acquire_ctx);
> +		if (ret) {
> +			ttm_bo_put(first_bo);
> +			return ret;
> +		}
> +		spin_lock(&glob->lru_lock);
> +		/* previous busy resv lock is held by above, idle now,
> +		 * so let them evictable.
> +		 */
> +		busy_ctx.interruptible = ctx->interruptible;
> +		busy_ctx.no_wait_gpu   = ctx->no_wait_gpu;
> +		busy_ctx.resv	       = first_bo->resv;
> +		busy_ctx.flags	       = TTM_OPT_FLAG_ALLOW_RES_EVICT;
> +
> +		bo = ttm_mem_find_evitable_bo(bdev, man, place, &busy_ctx, NULL,
> +					      &locked);
> +		if (bo && (bo->resv == first_bo->resv))
> +			locked = true;
> +		else if (bo)
> +			ww_mutex_unlock(&first_bo->resv->lock);
> +		if (!bo) {
> +			spin_unlock(&glob->lru_lock);
> +			ttm_bo_put(first_bo);
> +			return -EBUSY;
> +		}
>  	}
>  
>  	kref_get(&bo->list_kref);
> @@ -829,11 +902,15 @@ static int ttm_mem_evict_first(struct ttm_bo_device *bdev,
>  		ret = ttm_bo_cleanup_refs(bo, ctx->interruptible,
>  					  ctx->no_wait_gpu, locked);
>  		kref_put(&bo->list_kref, ttm_bo_release_list);
> +		if (first_bo)
> +			ttm_bo_put(first_bo);
>  		return ret;
>  	}
>  
>  	ttm_bo_del_from_lru(bo);
>  	spin_unlock(&glob->lru_lock);
> +	if (first_bo)
> +		ttm_bo_put(first_bo);
>  
>  	ret = ttm_bo_evict(bo, ctx);
>  	if (locked) {
> @@ -907,7 +984,7 @@ static int ttm_bo_mem_force_space(struct ttm_buffer_object *bo,
>  			return ret;
>  		if (mem->mm_node)
>  			break;
> -		ret = ttm_mem_evict_first(bdev, mem_type, place, ctx);
> +		ret = ttm_mem_evict_first(bdev, mem_type, place, ctx, bo->resv);
>  		if (unlikely(ret != 0))
>  			return ret;
>  	} while (1);
> @@ -1401,7 +1478,8 @@ static int ttm_bo_force_list_clean(struct ttm_bo_device *bdev,
>  	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
>  		while (!list_empty(&man->lru[i])) {
>  			spin_unlock(&glob->lru_lock);
> -			ret = ttm_mem_evict_first(bdev, mem_type, NULL, &ctx);
> +			ret = ttm_mem_evict_first(bdev, mem_type, NULL, &ctx,
> +						  NULL);
>  			if (ret)
>  				return ret;
>  			spin_lock(&glob->lru_lock);
> @@ -1772,7 +1850,8 @@ int ttm_bo_swapout(struct ttm_bo_global *glob, struct ttm_operation_ctx *ctx)
>  	spin_lock(&glob->lru_lock);
>  	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
>  		list_for_each_entry(bo, &glob->swap_lru[i], swap) {
> -			if (ttm_bo_evict_swapout_allowable(bo, ctx, &locked)) {
> +			if (ttm_bo_evict_swapout_allowable(bo, ctx, &locked,
> +							   NULL)) {
>  				ret = 0;
>  				break;
>  			}
> -- 
> 2.17.1
> 
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> dri-devel@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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