[PATCH/RESEND] arm64: defconfig: Enlarge CMA alignment to 2 MiB
Will Deacon
will.deacon at arm.com
Mon Feb 13 03:36:24 PST 2017
On Mon, Feb 13, 2017 at 12:04:18PM +0100, Geert Uytterhoeven 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 at glider.be>
> ---
> Is this useful?
I assume you're proposing it because you see an improvement? :)
> Should there instead be different defaults in Kconfig, depending on
> enabled platform support?
I don't object to updating defconfig as a quick hack, but the right solution
is probably to make the core Kconfig default value overridable by the
architecture.
Will
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