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Date: Wed, 1 Feb 2017 22:45:35 +0900 From: Magnus Damm <magnus.damm@...il.com> To: Geert Uytterhoeven <geert+renesas@...der.be> Cc: Marek Szyprowski <m.szyprowski@...sung.com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Linux-Renesas <linux-renesas-soc@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH/RFC] arm64: defconfig: Enlarge CMA alignment to 2 MiB Hi Geert, On Sat, Jan 28, 2017 at 1:03 AM, Geert Uytterhoeven <geert+renesas@...der.be> 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@...der.be> > --- > 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
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