On Tue, Apr 15, 2025 at 10:20 AM Juan Yescas jyescas@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@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@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