From: Peng Fan <peng.fan@nxp.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "will@kernel.org" <will@kernel.org>,
"nsaenzjulienne@suse.de" <nsaenzjulienne@suse.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
dl-linux-imx <linux-imx@nxp.com>,
Robin Murphy <robin.murphy@arm.com>
Subject: RE: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable without EXPERT
Date: Wed, 25 Mar 2020 00:34:15 +0000 [thread overview]
Message-ID: <AM0PR04MB44819E95EB1FABF09DEE682788CE0@AM0PR04MB4481.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20200324174134.GH3901@mbp>
> Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable
> without EXPERT
>
> On Tue, Mar 10, 2020 at 08:48:46PM +0800, peng.fan@nxp.com wrote:
> > From: Peng Fan <peng.fan@nxp.com>
> >
> > commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32")
> > enables both ZONE_DMA and ZONE_DMA32. The lower 1GB memory will
> be
> > occupied by ZONE_DMA, this will cause CMA allocation fail on some
> > platforms, because CMA area could not across different type of memory
> > zones.
> >
> > Make CONFIG_ZONE_DMA configurable without EXPERT option could let
> > people build non debug kernel image with CONFIG_ZONE_DMA disabled.
>
> While I see why you need to toggle this feature, I'd rather try to figure out
> whether there is a better solution that does not break the single kernel image
> aim (i.e. the same config works for all supported SoCs).
>
> When we decided to go ahead with a static 1GB ZONE_DMA for Raspberry Pi
> 4, we thought that other platforms would be fine, ZONE_DMA32 allocations
> fall back to ZONE_DMA. We missed the large CMA case.
>
> I see a few potential options:
>
> a) Ensure the CMA is contained within a single zone.
This will break legacy dts with new version kernel.
How large is it in
> your case?
It is 1GB
Is it allocated by the kernel dynamically or a fixed start
> set by the boot loader?
We use alloc-ranges and size in kernel dts.
But there is only 2GB DRAM in the board.
>
> b) Change the CMA allocator to allow spanning multiple zones (last time
> I looked it wasn't trivial since it relied on some per-zone lock).
>
> c) Make ZONE_DMA dynamic on arm64 and only enable it if RPi4.
Option c seems a bit easier to me :)
I will try to explore both, but if you have time to help, that would be
appreciated.
Thanks,
Peng.
>
> --
> Catalin
next prev parent reply other threads:[~2020-03-25 0:34 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-10 12:48 [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable without EXPERT peng.fan
2020-03-23 1:30 ` Peng Fan
2020-03-24 17:41 ` Catalin Marinas
2020-03-25 0:34 ` Peng Fan [this message]
2020-03-25 10:16 ` Catalin Marinas
2020-03-25 12:30 ` Peng Fan
2020-03-27 11:17 ` Nicolas Saenz Julienne
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