linux-kernel - Re: [PATCH v6 3/4] of: reserved_mem: Use unflatten_devicetree APIs to scan reserved memory nodes

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Message-ID: <1684910a-54e2-4df5-a076-de9c2de4277b@quicinc.com>
Date: Mon, 8 Jul 2024 16:12:14 -0700
From: Oreoluwa Babatunde <quic_obabatun@...cinc.com>
To: Klara Modin <klarasmodin@...il.com>, <robh@...nel.org>,
        <saravanak@...gle.com>, <hch@....de>, <m.szyprowski@...sung.com>,
        <robin.murphy@....com>, <will@...nel.org>, <catalin.marinas@....com>
CC: <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux.dev>, <kernel@...cinc.com>
Subject: Re: [PATCH v6 3/4] of: reserved_mem: Use unflatten_devicetree APIs to
 scan reserved memory nodes


On 7/5/2024 8:38 AM, Klara Modin wrote:
> On 2024-07-05 15:05, Klara Modin wrote:
>> Hi,
>>
>> On 2024-05-29 00:36, Oreoluwa Babatunde wrote:
>>> The unflatten_devicetree APIs have been setup and are available to be
>>> used by the time the fdt_init_reserved_mem() function is called.
>>> Since the unflatten_devicetree APIs are a more efficient way of scanning
>>> through the DT nodes, switch to using these APIs to facilitate the rest
>>> of the reserved memory processing.
>>
>> With this patch series, I've observed significantly less memory available to userspace on my Raspberry Pi 1 and 3.
>>
>> I see this message on the kernel console:
>> Jul  4 23:13:49 bonnet kernel: OF: reserved mem: 0x1b000000..0x1effffff (65536 KiB) map non-reusable linux
>>
>> where it was previously marked as reusable:
>> Jul  4 22:23:22 bonnet kernel: OF: reserved mem: 0x1b000000..0x1effffff (65536 KiB) map reusable linux,cma
>>
>> If I look at bcm283x.dtsi, it definitely has the reusable property.
>>
>> I've below pointed out the snippet I think could be suspicous.
>>
>>>
>>> Signed-off-by: Oreoluwa Babatunde <quic_obabatun@...cinc.com>
>>> ---
>>>   drivers/of/of_reserved_mem.c    | 93 ++++++++++++++++++++-------------
>>>   include/linux/of_reserved_mem.h |  2 +-
>>>   kernel/dma/coherent.c           | 10 ++--
>>>   kernel/dma/contiguous.c         |  8 +--
>>>   kernel/dma/swiotlb.c            | 10 ++--
>>>   5 files changed, 72 insertions(+), 51 deletions(-)
>>>
>>> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
>>> index 113d593ea031..05283cd24c3b 100644
>>> --- a/drivers/of/of_reserved_mem.c
>>> +++ b/drivers/of/of_reserved_mem.c
>
>>> @@ -447,7 +476,7 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
>>>                  uname, (unsigned long)(size / SZ_1M));
>>>           return -ENOMEM;
>>>       }
>>
>>
>>> -    fdt_reserved_mem_save_node(node, uname, base, size);
>>> +    fdt_reserved_mem_save_node(NULL, uname, base, size);
>>
>> This could perhaps be suspicious?
>>
>> The above message seems to come from of_init_reserved_mem_node when
>> called from of_reserved_mem_save_node when called from here. This would mean that the node is not actually saved to rmem and thus not marked reusable?
>>
>>
>>>       return 0;
>>>   }
>
>>
>> Regards,
>> Klara Modin
>
> Attaching kernel logs of old and new behavior, and my config for reference.
Hi Klara,

Thanks for pointing this out. I have uploaded a fix here:
https://lore.kernel.org/all/20240708230613.448846-1-quic_obabatun@quicinc.com/

Please test and see if this fixes the issue.

Thank you!
Oreoluwa