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J . Mercier" , =?UTF-8?q?Christian=20K=C3=B6nig?= , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, zhengtangquan@oppo.com, Barry Song Subject: [PATCH] dma-buf: system_heap: use larger contiguous mappings instead of per-page mmap Date: Sun, 31 Aug 2025 07:58:38 +0800 Message-Id: <20250830235838.58067-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song We can allocate high-order pages, but mapping them one by one is inefficient. This patch changes the code to map as large a chunk as possible. The code looks somewhat complicated mainly because supporting mmap with a non-zero offset is a bit tricky. Using the micro-benchmark below, we see that mmap becomes 3.5X faster: #include #include #include #include #include #include #include #include #define SIZE (512UL * 1024 * 1024) #define PAGE 4096 #define STRIDE (PAGE/sizeof(int)) #define PAGES (SIZE/PAGE) int main(void) { int heap =3D open("/dev/dma_heap/system", O_RDONLY); struct dma_heap_allocation_data d =3D { .len =3D SIZE, .fd_flags =3D = O_RDWR|O_CLOEXEC }; ioctl(heap, DMA_HEAP_IOCTL_ALLOC, &d); struct timespec t0, t1; clock_gettime(CLOCK_MONOTONIC, &t0); int *p =3D mmap(NULL, SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, d.fd, 0= ); clock_gettime(CLOCK_MONOTONIC, &t1); for (int i =3D 0; i < PAGES; i++) p[i*STRIDE] =3D i; for (int i =3D 0; i < PAGES; i++) if (p[i*STRIDE] !=3D i) { fprintf(stderr, "mismatch at page %d\n", i); exit(1); } long ns =3D (t1.tv_sec-t0.tv_sec)*1000000000L + (t1.tv_nsec-t0.tv_nse= c); printf("mmap 512MB took %.3f us, verify OK\n", ns/1000.0); return 0; } W/ patch: ~ # ./a.out mmap 512MB took 200266.000 us, verify OK ~ # ./a.out mmap 512MB took 198151.000 us, verify OK ~ # ./a.out mmap 512MB took 197069.000 us, verify OK ~ # ./a.out mmap 512MB took 196781.000 us, verify OK ~ # ./a.out mmap 512MB took 198102.000 us, verify OK ~ # ./a.out mmap 512MB took 195552.000 us, verify OK W/o patch: ~ # ./a.out mmap 512MB took 6987470.000 us, verify OK ~ # ./a.out mmap 512MB took 6970739.000 us, verify OK ~ # ./a.out mmap 512MB took 6984383.000 us, verify OK ~ # ./a.out mmap 512MB took 6971311.000 us, verify OK ~ # ./a.out mmap 512MB took 6991680.000 us, verify OK Signed-off-by: Barry Song Acked-by: John Stultz --- drivers/dma-buf/heaps/system_heap.c | 33 +++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 9 deletions(-) diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/sy= stem_heap.c index bbe7881f1360..4c782fe33fd4 100644 --- a/drivers/dma-buf/heaps/system_heap.c +++ b/drivers/dma-buf/heaps/system_heap.c @@ -186,20 +186,35 @@ static int system_heap_mmap(struct dma_buf *dmabuf, s= truct vm_area_struct *vma) struct system_heap_buffer *buffer =3D dmabuf->priv; struct sg_table *table =3D &buffer->sg_table; unsigned long addr =3D vma->vm_start; - struct sg_page_iter piter; - int ret; + unsigned long pgoff =3D vma->vm_pgoff; + struct scatterlist *sg; + int i, ret; + + for_each_sgtable_sg(table, sg, i) { + unsigned long n =3D sg->length >> PAGE_SHIFT; =20 - for_each_sgtable_page(table, &piter, vma->vm_pgoff) { - struct page *page =3D sg_page_iter_page(&piter); + if (pgoff < n) + break; + pgoff -=3D n; + } + + for (; sg && addr < vma->vm_end; sg =3D sg_next(sg)) { + unsigned long n =3D (sg->length >> PAGE_SHIFT) - pgoff; + struct page *page =3D sg_page(sg) + pgoff; + unsigned long size =3D n << PAGE_SHIFT; + + if (addr + size > vma->vm_end) + size =3D vma->vm_end - addr; =20 - ret =3D remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE, - vma->vm_page_prot); + ret =3D remap_pfn_range(vma, addr, page_to_pfn(page), + size, vma->vm_page_prot); if (ret) return ret; - addr +=3D PAGE_SIZE; - if (addr >=3D vma->vm_end) - return 0; + + addr +=3D size; + pgoff =3D 0; } + return 0; } =20 --=20 2.39.3 (Apple Git-146)