RE: [PATCH v6 7/7] udmabuf: reuse folio array when pin folios

[Kasireddy, Vivek]

Hi Huan,

> Subject: [PATCH v6 7/7] udmabuf: reuse folio array when pin folios
> 
> When invoke memfd_pin_folios, we need offer an array to save each folio
> which we pinned.
> 
> The currently way is dynamic alloc an array, get folios, save into
*current

> udmabuf and then free.
> 
> If the size is tiny(alloc from slab) is ok due to slab can cache it.
> Or, just PCP order can cover, also ok.
A casual reader may not know what is PCP. Please mention what it
stands for and how it is relevant here.

> 
> But if size is huge, need fallback into vmalloc, then, not well, due to
> each page need alloc, and map into vmalloc area. Too heavy.
I think it would be better if the above two lines are rewritten to more clearly
describe why or how fallback to vmalloc adversely affects performance.

Thanks,
Vivek

> 
> Now that we need to iter each udmabuf item, then pin it's range folios,
> we can reuse the maximum size range's folios array.
> 
> Signed-off-by: Huan Yang <link@xxxxxxxx>
> Acked-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
> ---
>  drivers/dma-buf/udmabuf.c | 36 +++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 0e405a589ca2..9fc5d22d54ae 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -341,28 +341,20 @@ static int export_udmabuf(struct udmabuf *ubuf,
>  }
> 
>  static long udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
> -			       loff_t start, loff_t size)
> +			       loff_t start, loff_t size, struct folio **folios)
>  {
>  	pgoff_t nr_pinned = ubuf->nr_pinned;
>  	pgoff_t upgcnt = ubuf->pagecount;
> -	struct folio **folios = NULL;
>  	u32 cur_folio, cur_pgcnt;
>  	pgoff_t pgoff, pgcnt;
>  	long nr_folios;
> -	long ret = 0;
>  	loff_t end;
> 
>  	pgcnt = size >> PAGE_SHIFT;
> -	folios = kvmalloc_array(pgcnt, sizeof(*folios), GFP_KERNEL);
> -	if (!folios)
> -		return -ENOMEM;
> -
>  	end = start + (pgcnt << PAGE_SHIFT) - 1;
>  	nr_folios = memfd_pin_folios(memfd, start, end, folios, pgcnt,
> &pgoff);
> -	if (nr_folios <= 0) {
> -		ret = nr_folios ? nr_folios : -EINVAL;
> -		goto end;
> -	}
> +	if (nr_folios <= 0)
> +		return nr_folios ? nr_folios : -EINVAL;
> 
>  	cur_pgcnt = 0;
>  	for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
> @@ -391,14 +383,15 @@ static long udmabuf_pin_folios(struct udmabuf
> *ubuf, struct file *memfd,
>  end:
>  	ubuf->pagecount = upgcnt;
>  	ubuf->nr_pinned = nr_pinned;
> -	kvfree(folios);
> -	return ret;
> +	return 0;
>  }
> 
>  static long udmabuf_create(struct miscdevice *device,
>  			   struct udmabuf_create_list *head,
>  			   struct udmabuf_create_item *list)
>  {
> +	unsigned long max_nr_folios = 0;
> +	struct folio **folios = NULL;
>  	pgoff_t pgcnt = 0, pglimit;
>  	struct udmabuf *ubuf;
>  	long ret = -EINVAL;
> @@ -410,14 +403,19 @@ static long udmabuf_create(struct miscdevice
> *device,
> 
>  	pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
>  	for (i = 0; i < head->count; i++) {
> +		pgoff_t subpgcnt;
> +
>  		if (!PAGE_ALIGNED(list[i].offset))
>  			goto err_noinit;
>  		if (!PAGE_ALIGNED(list[i].size))
>  			goto err_noinit;
> 
> -		pgcnt += list[i].size >> PAGE_SHIFT;
> +		subpgcnt = list[i].size >> PAGE_SHIFT;
> +		pgcnt += subpgcnt;
>  		if (pgcnt > pglimit)
>  			goto err_noinit;
> +
> +		max_nr_folios = max_t(unsigned long, subpgcnt,
> max_nr_folios);
>  	}
> 
>  	if (!pgcnt)
> @@ -427,6 +425,12 @@ static long udmabuf_create(struct miscdevice
> *device,
>  	if (ret)
>  		goto err;
> 
> +	folios = kvmalloc_array(max_nr_folios, sizeof(*folios), GFP_KERNEL);
> +	if (!folios) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
>  	for (i = 0; i < head->count; i++) {
>  		struct file *memfd = fget(list[i].memfd);
> 
> @@ -442,7 +446,7 @@ static long udmabuf_create(struct miscdevice
> *device,
>  		}
> 
>  		ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
> -					 list[i].size);
> +					 list[i].size, folios);
>  		fput(memfd);
>  		if (ret)
>  			goto err;
> @@ -453,12 +457,14 @@ static long udmabuf_create(struct miscdevice
> *device,
>  	if (ret < 0)
>  		goto err;
> 
> +	kvfree(folios);
>  	return ret;
> 
>  err:
>  	deinit_udmabuf(ubuf);
>  err_noinit:
>  	kfree(ubuf);
> +	kvfree(folios);
>  	return ret;
>  }
> 
> --
> 2.45.2