linux-kernel - Re: [PATCH v6 3/4] arm64: use both ZONE_DMA and ZONE

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Date:   Mon, 21 Oct 2019 10:46:23 -0400
From:   Qian Cai <cai@....pw>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     f.fainelli@...il.com, mbrugger@...e.com, marc.zyngier@....com,
        catalin.marinas@....com, Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Rob Herring <robh+dt@...nel.org>, wahrenst@....net,
        m.szyprowski@...sung.com, phill@...pberrypi.org, will@...nel.org,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 3/4] arm64: use both ZONE_DMA and ZONE_DMA32



> On Oct 21, 2019, at 10:34 AM, Nicolas Saenz Julienne <nsaenzjulienne@...e.de> wrote:
> 
> On Mon, 2019-10-21 at 10:15 -0400, Qian Cai wrote:
>>> On Sep 11, 2019, at 2:25 PM, Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
>>> wrote:
>>> 
>>> So far all arm64 devices have supported 32 bit DMA masks for their
>>> peripherals. This is not true anymore for the Raspberry Pi 4 as most of
>>> it's peripherals can only address the first GB of memory on a total of
>>> up to 4 GB.
>>> 
>>> This goes against ZONE_DMA32's intent, as it's expected for ZONE_DMA32
>>> to be addressable with a 32 bit mask. So it was decided to re-introduce
>>> ZONE_DMA in arm64.
>>> 
>>> ZONE_DMA will contain the lower 1G of memory, which is currently the
>>> memory area addressable by any peripheral on an arm64 device.
>>> ZONE_DMA32 will contain the rest of the 32 bit addressable memory.
>>> 
>>> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
>>> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
>>> 
>>> ---
>> 
>> With ZONE_DMA=y, this config will fail to reserve 512M CMA on a server,
>> 
>> https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config
>> 
>> CONFIG_DMA_CMA=y
>> CONFIG_CMA_SIZE_MBYTES=64
>> CONFIG_CMA_SIZE_SEL_MBYTES=y
>> CONFIG_CMA_ALIGNMENT=8
>> CONFIG_CMA=y
>> CONFIG_CMA_DEBUGFS=y
>> CONFIG_CMA_AREAS=7
>> 
>> Is this expected?
> 
> Not really, just tested cma=512M on a Raspberry Pi4, and it went well. The only
> thing on my build that differs from your config is CONFIG_CMA_DEBUGFS.
> 
> Could you post more information on the device you're experiencing this on? Also
> some logs.

With the above config, it does not even need "cma=512M" kernel cmdline.

[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x431f0af1]
[    0.000000] Linux version 5.4.0-rc4-next-20191021+ (clang version 8.0.1 (Red Hat 8.0.1-1.module+el8.1.0+3866+6be7f4d8)) #1 SMP Mon Oct 21 10:03:03 EDT 2019
[    0.000000] Setting debug_guardpage_minorder to 1
[    0.000000] efi: Getting EFI parameters from FDT:
[    0.000000] efi: EFI v2.70 by American Megatrends
[    0.000000] efi:  ESRT=0xf935ed98  SMBIOS=0xfcc90000  SMBIOS 3.0=0xfcc80000  ACPI 2.0=0xfac80000  MEMRESERVE=0xfacd1018 
[    0.000000] esrt: Reserving ESRT space from 0x00000000f935ed98 to 0x00000000f935edd0.
[    0.000000] crashkernel reserved: 0x00000097db400000 - 0x00000097fb400000 (512 MB)
[    0.000000] cma: Reserved 512 MiB at 0x00000000a0000000

With ZONE_DMA=y, it will say,

cma: Failed to reserve 512 MiB

The machine is a ThunderX2 server.

https://buy.hpe.com/us/en/servers/apollo-systems/apollo-70-system/apollo-70-system/hpe-apollo-70-system/p/1010742472

# lscpu
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              256
On-line CPU(s) list: 0-255
Thread(s) per core:  4
Core(s) per socket:  32
Socket(s):           2
NUMA node(s):        2
Vendor ID:           Cavium
Model:               1
Model name:          ThunderX2 99xx
Stepping:            0x1
BogoMIPS:            400.00
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            32768K
NUMA node0 CPU(s):   0-127
NUMA node1 CPU(s):   128-255
Flags:               fp asimd aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm