linux-kernel - Re: [PATCH] dma-buf: system_heap: No separate allocation for attachment sg

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Message-ID: <a4f72149-70a0-4bbe-bdcc-70384c152f83@amd.com>
Date: Tue, 22 Apr 2025 10:24:45 +0200
From: Christian König <christian.koenig@....com>
To: "T.J. Mercier" <tjmercier@...gle.com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Benjamin Gaignard <benjamin.gaignard@...labora.com>,
 Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-buf: system_heap: No separate allocation for
 attachment sg_tables

Am 17.04.25 um 20:09 schrieb T.J. Mercier:
> struct dma_heap_attachment is a separate allocation from the struct
> sg_table it contains, but there is no reason for this. Let's use the
> slab allocator just once instead of twice for dma_heap_attachment.
>
> Signed-off-by: T.J. Mercier <tjmercier@...gle.com>

I'm not *that* expert for this code, but looks totally reasonable to me.

Reviewed-by: Christian König <christian.koenig@....com>

Let me know if I should push that to drm-misc-next.

Regards,
Christian.

> ---
>  drivers/dma-buf/heaps/system_heap.c | 43 ++++++++++++-----------------
>  1 file changed, 17 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 26d5dc89ea16..bee10c400cf0 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -35,7 +35,7 @@ struct system_heap_buffer {
>  
>  struct dma_heap_attachment {
>  	struct device *dev;
> -	struct sg_table *table;
> +	struct sg_table table;
>  	struct list_head list;
>  	bool mapped;
>  };
> @@ -54,29 +54,22 @@ static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
>  static const unsigned int orders[] = {8, 4, 0};
>  #define NUM_ORDERS ARRAY_SIZE(orders)
>  
> -static struct sg_table *dup_sg_table(struct sg_table *table)
> +static int dup_sg_table(struct sg_table *from, struct sg_table *to)
>  {
> -	struct sg_table *new_table;
> -	int ret, i;
>  	struct scatterlist *sg, *new_sg;
> +	int ret, i;
>  
> -	new_table = kzalloc(sizeof(*new_table), GFP_KERNEL);
> -	if (!new_table)
> -		return ERR_PTR(-ENOMEM);
> -
> -	ret = sg_alloc_table(new_table, table->orig_nents, GFP_KERNEL);
> -	if (ret) {
> -		kfree(new_table);
> -		return ERR_PTR(-ENOMEM);
> -	}
> +	ret = sg_alloc_table(to, from->orig_nents, GFP_KERNEL);
> +	if (ret)
> +		return ret;
>  
> -	new_sg = new_table->sgl;
> -	for_each_sgtable_sg(table, sg, i) {
> +	new_sg = to->sgl;
> +	for_each_sgtable_sg(from, sg, i) {
>  		sg_set_page(new_sg, sg_page(sg), sg->length, sg->offset);
>  		new_sg = sg_next(new_sg);
>  	}
>  
> -	return new_table;
> +	return 0;
>  }
>  
>  static int system_heap_attach(struct dma_buf *dmabuf,
> @@ -84,19 +77,18 @@ static int system_heap_attach(struct dma_buf *dmabuf,
>  {
>  	struct system_heap_buffer *buffer = dmabuf->priv;
>  	struct dma_heap_attachment *a;
> -	struct sg_table *table;
> +	int ret;
>  
>  	a = kzalloc(sizeof(*a), GFP_KERNEL);
>  	if (!a)
>  		return -ENOMEM;
>  
> -	table = dup_sg_table(&buffer->sg_table);
> -	if (IS_ERR(table)) {
> +	ret = dup_sg_table(&buffer->sg_table, &a->table);
> +	if (ret) {
>  		kfree(a);
> -		return -ENOMEM;
> +		return ret;
>  	}
>  
> -	a->table = table;
>  	a->dev = attachment->dev;
>  	INIT_LIST_HEAD(&a->list);
>  	a->mapped = false;
> @@ -120,8 +112,7 @@ static void system_heap_detach(struct dma_buf *dmabuf,
>  	list_del(&a->list);
>  	mutex_unlock(&buffer->lock);
>  
> -	sg_free_table(a->table);
> -	kfree(a->table);
> +	sg_free_table(&a->table);
>  	kfree(a);
>  }
>  
> @@ -129,7 +120,7 @@ static struct sg_table *system_heap_map_dma_buf(struct dma_buf_attachment *attac
>  						enum dma_data_direction direction)
>  {
>  	struct dma_heap_attachment *a = attachment->priv;
> -	struct sg_table *table = a->table;
> +	struct sg_table *table = &a->table;
>  	int ret;
>  
>  	ret = dma_map_sgtable(attachment->dev, table, direction, 0);
> @@ -164,7 +155,7 @@ static int system_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
>  	list_for_each_entry(a, &buffer->attachments, list) {
>  		if (!a->mapped)
>  			continue;
> -		dma_sync_sgtable_for_cpu(a->dev, a->table, direction);
> +		dma_sync_sgtable_for_cpu(a->dev, &a->table, direction);
>  	}
>  	mutex_unlock(&buffer->lock);
>  
> @@ -185,7 +176,7 @@ static int system_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
>  	list_for_each_entry(a, &buffer->attachments, list) {
>  		if (!a->mapped)
>  			continue;
> -		dma_sync_sgtable_for_device(a->dev, a->table, direction);
> +		dma_sync_sgtable_for_device(a->dev, &a->table, direction);
>  	}
>  	mutex_unlock(&buffer->lock);
>  
>
> base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444