Some IOMMUs (e.g. Renesas IPMMU/VMSA) support only page sizes of 4 KiB, 2 MiB, and 1 GiB.
With the default setting of CONFIG_CMA_ALIGNMENT = 8, allocations larger than 1 MiB are aligned to a 1 MiB boundary only. Hence a 2 MiB allocation may not be aligned, leading to a mapping of 512 4 KiB pages. Increase CONFIG_CMA_ALIGNMENT to allow mapping a 2 MiB buffer using a single PTE, decreasing memory usage and TLB pressure. Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be> --- Is this useful? Should there instead be different defaults in Kconfig, depending on enabled platform support? --- arch/arm64/configs/defconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig index cea17afae855f589..1acc422052050770 100644 --- a/arch/arm64/configs/defconfig +++ b/arch/arm64/configs/defconfig @@ -143,6 +143,7 @@ CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug" CONFIG_DEVTMPFS=y CONFIG_DEVTMPFS_MOUNT=y CONFIG_DMA_CMA=y +CONFIG_CMA_ALIGNMENT=9 CONFIG_MTD=y CONFIG_MTD_M25P80=y CONFIG_MTD_SPI_NOR=y -- 1.9.1
