[RFC] dma-buf: system_heap: add PTE_CONT for larger contiguous

[gao xu]

commit 04c7adb5871a ("dma-buf: system_heap: use larger contiguous mappings
instead of per-page mmap") facilitates the use of PTE_CONT. The system_heap
allocates pages of order 4 and 8 that meet the alignment requirements for
PTE_CONT. enabling PTE_CONT for larger contiguous mappings.

After applying this patch, TLB misses are reduced by approximately 5% when
opening the camera on Android systems.

Signed-off-by: gao xu <gaoxu2@xxxxxxxxx>
---
 drivers/dma-buf/heaps/system_heap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 4c782fe33..103b06f89 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -202,12 +202,16 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 		unsigned long n = (sg->length >> PAGE_SHIFT) - pgoff;
 		struct page *page = sg_page(sg) + pgoff;
 		unsigned long size = n << PAGE_SHIFT;
+		pgprot_t prot = vma->vm_page_prot;
 
 		if (addr + size > vma->vm_end)
 			size = vma->vm_end - addr;
 
+		if (((addr | size) & ~CONT_PTE_MASK) == 0)
+			prot = __pgprot(pgprot_val(prot) | PTE_CONT);
+
 		ret = remap_pfn_range(vma, addr, page_to_pfn(page),
-				size, vma->vm_page_prot);
+				size, prot);
 		if (ret)
 			return ret;
 
-- 
2.42.0