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

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, May 15, 2019 at 10:38:28AM +0200, Daniel Vetter wrote:
> 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.

Ofc this is meant as a comment on the entire patch series, without all the
other patches to make sure BO always stay on a relevant LRU there's still
gaps in the guaranteed forward progress eviction algorithm.
-Daniel

> -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
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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