linux-kernel - Re: [PATCH 2/4] arm64: defconfig: Set cma heap size to 128MB

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Message-ID: <CAFGCpxyNubwm1kyjH2kSGGchSTuL7oqD4J=_frhXecrgvEVU=w@mail.gmail.com>
Date:   Wed, 24 Aug 2016 10:23:06 +0800
From:   Guodong Xu <guodong.xu@...aro.org>
To:     Thierry Reding <treding@...dia.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, horms+renesas@...ge.net.au,
        Olof Johansson <olof@...om.net>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Xu Wei <xuwei5@...ilicon.com>, khilman@...libre.com,
        Riku Voipio <riku.voipio@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xinliang Liu <xinliang.liu@...aro.org>
Subject: Re: [PATCH 2/4] arm64: defconfig: Set cma heap size to 128MB

On 22 August 2016 at 17:06, Thierry Reding <treding@...dia.com> wrote:
> On Fri, Aug 19, 2016 at 11:42:06PM +0800, Guodong Xu wrote:
>> From: Xinliang Liu <xinliang.liu@...aro.org>
>>
>> For debian linux, cma heap is used to allocate graphic buffers.
>> The default size is 16 MB which is not enought.
>> So increase the size to 128 MB.
>>
>> Signed-off-by: Xinliang Liu <xinliang.liu@...aro.org>
>> ---
>>  arch/arm64/configs/defconfig | 1 +
>>  1 file changed, 1 insertion(+)
>
> This is a bad idea. You're increasing this heap for all users of the
> default configuration (which on 64-bit ARM is everyone, really). Many of
> the devices don't require the CMA except maybe for the occasional very
> small buffer. Most implement some form of IOMMU support that removes the
> need for large amounts of contiguous physical memory.
>
> I think it's a better idea to have some bootloader append a cma=128 to
> the kernel command-line if necessary.
>

I will remove this. Thanks.

-Guodong Xu

> Thierry