[PATCH v5 6/7] udmabuf: remove udmabuf_folio

[Kasireddy, Vivek]

Hi Huan,

> Subject: [PATCH v5 6/7] udmabuf: remove udmabuf_folio
> 
> Currently, udmabuf handles folio by creating an unpin list to record
> each folio obtained from the list and unpinning them when released. To
> maintain this approach, many data structures have been established.
> 
> However, maintaining this type of data structure requires a significant
> amount of memory and traversing the list is a substantial overhead,
> which is not friendly to the CPU cache.
> 
> Considering that during creation, we arranged the folio array in the
> order of pin and set the offset according to pgcnt.
> 
> We actually don't need to use unpin_list to unpin during release.
> Instead, we can iterate through the folios array during release and
> unpin any folio that is different from the ones previously accessed.
> 
> By this, not only saves the overhead of the udmabuf_folio data structure
> but also makes array access more cache-friendly.
> 
> Signed-off-by: Huan Yang <link at vivo.com>
> ---
>  drivers/dma-buf/udmabuf.c | 65 +++++++++++++++++----------------------
>  1 file changed, 29 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 254d9ec3d9f3..d449c1fd67a5 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -27,15 +27,21 @@ MODULE_PARM_DESC(size_limit_mb, "Max size of a
> dmabuf, in megabytes. Default is
>  struct udmabuf {
>  	pgoff_t pagecount;
>  	struct folio **folios;
> +
> +	/**
> +	 * Unlike folios, pinned_folios is only used for unpin.
> +	 * So, nr_pinned is not the same to pagecount, the pinned_folios
> +	 * only set each folio which already pinned when udmabuf_create.
> +	 * Note that, since a folio may be pinned multiple times, each folio
> +	 * can be added to pinned_folios multiple times, depending on how
> many
> +	 * times the folio has been pinned when create.
> +	 */
> +	pgoff_t nr_pinned;
> +	struct folio **pinned_folios;
> +
>  	struct sg_table *sg;
>  	struct miscdevice *device;
>  	pgoff_t *offsets;
> -	struct list_head unpin_list;
> -};
> -
> -struct udmabuf_folio {
> -	struct folio *folio;
> -	struct list_head list;
>  };
> 
>  static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
> @@ -198,38 +204,18 @@ static void unmap_udmabuf(struct
> dma_buf_attachment *at,
>  	return put_sg_table(at->dev, sg, direction);
>  }
> 
> -static void unpin_all_folios(struct list_head *unpin_list)
> +static void unpin_all_folios(struct udmabuf *ubuf)
>  {
> -	struct udmabuf_folio *ubuf_folio;
> +	pgoff_t i;
> 
> -	while (!list_empty(unpin_list)) {
> -		ubuf_folio = list_first_entry(unpin_list,
> -					      struct udmabuf_folio, list);
> -		unpin_folio(ubuf_folio->folio);
> +	for (i = 0; i < ubuf->nr_pinned; ++i)
> +		unpin_folio(ubuf->pinned_folios[i]);
> 
> -		list_del(&ubuf_folio->list);
> -		kfree(ubuf_folio);
> -	}
> -}
> -
> -static int add_to_unpin_list(struct list_head *unpin_list,
> -			     struct folio *folio)
> -{
> -	struct udmabuf_folio *ubuf_folio;
> -
> -	ubuf_folio = kzalloc(sizeof(*ubuf_folio), GFP_KERNEL);
> -	if (!ubuf_folio)
> -		return -ENOMEM;
> -
> -	ubuf_folio->folio = folio;
> -	list_add_tail(&ubuf_folio->list, unpin_list);
> -	return 0;
> +	kvfree(ubuf->pinned_folios);
>  }
> 
>  static __always_inline int init_udmabuf(struct udmabuf *ubuf, pgoff_t
> pgcnt)
>  {
> -	INIT_LIST_HEAD(&ubuf->unpin_list);
> -
>  	ubuf->folios = kvmalloc_array(pgcnt, sizeof(*ubuf->folios),
> GFP_KERNEL);
>  	if (!ubuf->folios)
>  		return -ENOMEM;
> @@ -238,12 +224,18 @@ static __always_inline int init_udmabuf(struct
> udmabuf *ubuf, pgoff_t pgcnt)
>  	if (!ubuf->offsets)
>  		return -ENOMEM;
> 
> +	ubuf->pinned_folios = kvmalloc_array(pgcnt,
> +					     sizeof(*ubuf->pinned_folios),
> +					     GFP_KERNEL);
> +	if (!ubuf->pinned_folios)
> +		return -ENOMEM;
> +
>  	return 0;
>  }
> 
>  static __always_inline void deinit_udmabuf(struct udmabuf *ubuf)
>  {
> -	unpin_all_folios(&ubuf->unpin_list);
> +	unpin_all_folios(ubuf);
>  	kvfree(ubuf->offsets);
>  	kvfree(ubuf->folios);
>  }
> @@ -353,7 +345,9 @@ static int export_udmabuf(struct udmabuf *ubuf,
>  static int udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
>  			      loff_t start, loff_t size)
>  {
> -	pgoff_t pgoff, pgcnt, upgcnt = ubuf->pagecount;
> +	pgoff_t pgoff, pgcnt;
> +	pgoff_t upgcnt = ubuf->pagecount;
> +	pgoff_t nr_pinned = ubuf->nr_pinned;
Reverse xmas style is preferred; please try to use that.

>  	u32 cur_folio, cur_pgcnt;
>  	struct folio **folios = NULL;
>  	long nr_folios;
> @@ -377,9 +371,7 @@ static int udmabuf_pin_folios(struct udmabuf *ubuf,
> struct file *memfd,
>  		pgoff_t subpgoff = pgoff;
>  		size_t fsize = folio_size(folios[cur_folio]);
> 
> -		ret = add_to_unpin_list(&ubuf->unpin_list, folios[cur_folio]);
> -		if (ret < 0)
> -			goto err;
> +		ubuf->pinned_folios[nr_pinned++] = folios[cur_folio];
> 
>  		for (; subpgoff < fsize; subpgoff += PAGE_SIZE) {
>  			ubuf->folios[upgcnt] = folios[cur_folio];
> @@ -399,6 +391,7 @@ static int udmabuf_pin_folios(struct udmabuf *ubuf,
> struct file *memfd,
>  end:
>  err:
>  	ubuf->pagecount = upgcnt;
> +	ubuf->nr_pinned = nr_pinned;
Acked-by: Vivek Kasireddy <vivek.kasireddy at intel.com>

>  	kvfree(folios);
>  	return ret;
>  }
> --
> 2.45.2