linux-kernel - Re: [PATCH] LoongArch: mm: Set max_pfn with the PFN of the last page

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Message-ID: <CAAhV-H7ZAK15ob3M=5eQrOhPvkSFhkrmVHd-mn6RXgQqQV_Ebg@mail.gmail.com>
Date: Tue, 4 Mar 2025 20:25:05 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: mm: Set max_pfn with the PFN of the last page

Hi, Bibo,

On Tue, Mar 4, 2025 at 7:27 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> The current max_pfn equals to zero. In this case, it caused users cannot
> get some page information through /proc such as kpagecount. The following
> message is displayed by stress-ng test suite with the command
> "stress-ng --verbose --physpage 1 -t 1".
>
>  # stress-ng --verbose --physpage 1 -t 1
>  stress-ng: error: [1691] physpage: cannot read page count for address 0x134ac000 in /proc/kpagecount, errno=22 (Invalid argument)
>  stress-ng: error: [1691] physpage: cannot read page count for address 0x7ffff207c3a8 in /proc/kpagecount, errno=22 (Invalid argument)
>  stress-ng: error: [1691] physpage: cannot read page count for address 0x134b0000 in /proc/kpagecount, errno=22 (Invalid argument)
>  ...
>
> After applying this patch, the kernel can pass the test.
>  # stress-ng --verbose --physpage 1 -t 1
>  stress-ng: debug: [1701] physpage: [1701] started (instance 0 on CPU 3)
>  stress-ng: debug: [1701] physpage: [1701] exited (instance 0 on CPU 3)
>  stress-ng: debug: [1700] physpage: [1701] terminated (success)
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
I think this patch are mainly fix commit
ff6c3d81f2e86b63a3a530683f89ef39 ("NUMA: optimize detection of memory
with no node id assigned by firmware"). So it is better to add a
Fixes: tag and Cc stable.

And the patch itself can be improved. there are three cases of
calculating max_low_pfn:
ACPI with NUMA, handled in numa.c
ACPI without NUMA, handled in mem.c
FDT, handled in setup.c

You have missed the 2nd case. The simplest way is add "max_pfn =
max_low_pfn" at the beginning of arch_mem_init() because all cases can
be handled here.

Huacai

> ---
>  arch/loongarch/kernel/numa.c  | 2 +-
>  arch/loongarch/kernel/setup.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
> index 84fe7f854820..002dbe62b329 100644
> --- a/arch/loongarch/kernel/numa.c
> +++ b/arch/loongarch/kernel/numa.c
> @@ -356,7 +356,7 @@ int __init init_numa_memory(void)
>                 node_mem_init(node);
>                 node_set_online(node);
>         }
> -       max_low_pfn = PHYS_PFN(memblock_end_of_DRAM());
> +       max_low_pfn = max_pfn = PHYS_PFN(memblock_end_of_DRAM());
>
>         setup_nr_node_ids();
>         loongson_sysconf.nr_nodes = nr_node_ids;
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index edcfdfcad7d2..ab8c9336d8f5 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -294,7 +294,7 @@ static void __init fdt_setup(void)
>         early_init_dt_scan(fdt_pointer, __pa(fdt_pointer));
>         early_init_fdt_reserve_self();
>
> -       max_low_pfn = PFN_PHYS(memblock_end_of_DRAM());
> +       max_low_pfn = max_pfn = PFN_PHYS(memblock_end_of_DRAM());
>  #endif
>  }
>
> --
> 2.39.3
>