[PATCH] dma-buf: heaps: Set allocation orders for larger page sizes

[T.J. Mercier]

On Tue, Apr 15, 2025 at 10:20 AM Juan Yescas <jyescas at google.com> wrote:
>
> This change sets the allocation orders for the different page sizes
> (4k, 16k, 64k) based on PAGE_SHIFT. Before this change, the orders
> for large page sizes were calculated incorrectly, this caused system
> heap to allocate from 2% to 4% more memory on 16KiB page size kernels.
>
> This change was tested on 4k/16k page size kernels.
>
> Signed-off-by: Juan Yescas <jyescas at google.com>

I think "dma-buf: system_heap:" would be better for the subject since
this is specific to the system heap.

Would you mind cleaning up the extra space on line 321 too?
@@ -318,7 +318,7 @@ static struct page
*alloc_largest_available(unsigned long size,
        int i;

        for (i = 0; i < NUM_ORDERS; i++) {
-               if (size <  (PAGE_SIZE << orders[i]))
+               if (size < (PAGE_SIZE << orders[i]))

With that,
Reviewed-by: T.J. Mercier <tjmercier at google.com>

Fixes: d963ab0f15fb ("dma-buf: system_heap: Allocate higher order
pages if available") is also probably a good idea.

> ---
>  drivers/dma-buf/heaps/system_heap.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 26d5dc89ea16..54674c02dcb4 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -50,8 +50,15 @@ static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
>   * to match with the sizes often found in IOMMUs. Using order 4 pages instead
>   * of order 0 pages can significantly improve the performance of many IOMMUs
>   * by reducing TLB pressure and time spent updating page tables.
> + *
> + * Note: When the order is 0, the minimum allocation is PAGE_SIZE. The possible
> + * page sizes for ARM devices could be 4K, 16K and 64K.
>   */
> -static const unsigned int orders[] = {8, 4, 0};
> +#define ORDER_1M (20 - PAGE_SHIFT)
> +#define ORDER_64K (16 - PAGE_SHIFT)
> +#define ORDER_FOR_PAGE_SIZE (0)
> +static const unsigned int orders[] = {ORDER_1M, ORDER_64K, ORDER_FOR_PAGE_SIZE};
> +
>  #define NUM_ORDERS ARRAY_SIZE(orders)
>
>  static struct sg_table *dup_sg_table(struct sg_table *table)
> --
> 2.49.0.604.gff1f9ca942-goog
>