Hi Geert, On Sat, Jan 28, 2017 at 1:03 AM, Geert Uytterhoeven <geert+renesas@xxxxxxxxx> wrote: > 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+renesas@xxxxxxxxx> > --- > Is this useful? > > Should there instead be different defaults in Kconfig, depending on > enabled platform support? I think there is a dependency on the kernel page size configuration as well. In case of 16 KiB or 64 KiB page size configuration other large page sizes may be required. Thanks, / magnus
