From: Peng Fan <[email protected]>
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.
Signed-off-by: Peng Fan <[email protected]>
---
arch/arm64/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 217e12ff2115..c4ba8bf011e1 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -270,7 +270,7 @@ config GENERIC_CALIBRATE_DELAY
def_bool y
config ZONE_DMA
- bool "Support DMA zone" if EXPERT
+ bool "Support DMA zone"
default y
config ZONE_DMA32
--
2.16.4
> Subject: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable
> without EXPERT
Gentle ping..
Thanks,
Peng.
>
> From: Peng Fan <[email protected]>
>
> 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.
>
> Signed-off-by: Peng Fan <[email protected]>
> ---
> arch/arm64/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index
> 217e12ff2115..c4ba8bf011e1 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -270,7 +270,7 @@ config GENERIC_CALIBRATE_DELAY
> def_bool y
>
> config ZONE_DMA
> - bool "Support DMA zone" if EXPERT
> + bool "Support DMA zone"
> default y
>
> config ZONE_DMA32
> --
> 2.16.4
On Tue, Mar 10, 2020 at 08:48:46PM +0800, [email protected] wrote:
> From: Peng Fan <[email protected]>
>
> 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. How large is it in
your case? Is it allocated by the kernel dynamically or a fixed start
set by the boot loader?
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.
--
Catalin
> Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable
> without EXPERT
>
> On Tue, Mar 10, 2020 at 08:48:46PM +0800, [email protected] wrote:
> > From: Peng Fan <[email protected]>
> >
> > 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
On Wed, Mar 25, 2020 at 12:34:15AM +0000, Peng Fan wrote:
> > On Tue, Mar 10, 2020 at 08:48:46PM +0800, [email protected] wrote:
> > > From: Peng Fan <[email protected]>
> > >
> > > 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.
So I guess without changing the dts, option (a) doesn't really work.
> > 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.
I don't have time but option (c) was already discussed and there are
patches from Nicolas on the list:
https://lore.kernel.org/linux-arm-kernel/[email protected]/
The above series was checking whether the platform is RPi4 and limiting
the ZONE_DMA size to 1GB (otherwise 4GB with ZONE_DMA32 empty). We ended
up with a static 1GB for ZONE_DMA but we missed the fact that it may
break existing platforms.
So I don't think it would be too hard to revive the above series (most
of it was already merged).
--
Catalin
> Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable
> without EXPERT
>
> On Wed, Mar 25, 2020 at 12:34:15AM +0000, Peng Fan wrote:
> > > On Tue, Mar 10, 2020 at 08:48:46PM +0800, [email protected] wrote:
> > > > From: Peng Fan <[email protected]>
> > > >
> > > > 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.
>
> So I guess without changing the dts, option (a) doesn't really work.
>
> > > 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.
>
> I don't have time but option (c) was already discussed and there are patches
> from Nicolas on the list:
>
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flinux-arm-kernel%2F20190820145821.27214-5-nsaenzjulienne%
> 40suse.de%2F&data=02%7C01%7Cpeng.fan%40nxp.com%7C6403ddf37
> 89b452ae5ee08d7d0a5a659%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
> %7C0%7C637207282191026738&sdata=t2cZ9HTCcRuaL9RO4kD%2BzN
> 2n4VqM%2F66zYNZIOComCVs%3D&reserved=0
>
> The above series was checking whether the platform is RPi4 and limiting the
> ZONE_DMA size to 1GB (otherwise 4GB with ZONE_DMA32 empty). We
> ended up with a static 1GB for ZONE_DMA but we missed the fact that it may
> break existing platforms.
Thanks for the information. I'll check the patchset and work out something
proper to fix the issue I met.
Thanks,
Peng.
>
> So I don't think it would be too hard to revive the above series (most of it was
> already merged).
>
> --
> Catalin
Hi Peng,
On Wed, 2020-03-25 at 12:30 +0000, Peng Fan wrote:
> > > > 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.
> >
> > So I guess without changing the dts, option (a) doesn't really work.
> >
> > > > 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).
I like this as a solution, ultimately why should CMA be linked to a specific
zone. Also, crossing the ZONE_DMA/ZONE_DMA32 boundary shouldn't be an issue
since we already default to ZONE_DMA32 as the default area for CMA.
That said, easier said than done.
> > > > 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.
> >
> > I don't have time but option (c) was already discussed and there are patches
> > from Nicolas on the list:
> >
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> > rnel.org%2Flinux-arm-kernel%2F20190820145821.27214-5-nsaenzjulienne%
> > 40suse.de%2F&data=02%7C01%7Cpeng.fan%40nxp.com%7C6403ddf37
> > 89b452ae5ee08d7d0a5a659%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
> > %7C0%7C637207282191026738&sdata=t2cZ9HTCcRuaL9RO4kD%2BzN
> > 2n4VqM%2F66zYNZIOComCVs%3D&reserved=0
> >
> > The above series was checking whether the platform is RPi4 and limiting the
> > ZONE_DMA size to 1GB (otherwise 4GB with ZONE_DMA32 empty). We
> > ended up with a static 1GB for ZONE_DMA but we missed the fact that it may
> > break existing platforms.
>
> Thanks for the information. I'll check the patchset and work out something
> proper to fix the issue I met.
Just an FYI, I'm follwing the conversation, and will try to look into as soon
as I get some free time. In the meantime if you want me to test/review anything
on the Raspberry Pi, I'll be happy to.
Regards,
Nicolas