linux-kernel - Re: [PATCH 2/3] LoongArch: Code cleanup in function pcpu_populate

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Date:   Tue, 1 Aug 2023 09:18:22 +0800
From:   bibo mao <maobibo@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, WANG Xuerui <kernel@...0n.name>
Subject: Re: [PATCH 2/3] LoongArch: Code cleanup in function pcpu_populate_pte



在 2023/7/31 22:15, Huacai Chen 写道:
> On Wed, Jul 12, 2023 at 11:16 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>> There are some code cleanups in function pcpu_populate_pte:
>> 1. Replace memblock_alloc with memblock_alloc_raw for pud and pmd since
>> they will be reinitialized with pud_init and pmd_init.
>>
>> 2. Add memory allocation failure handling
>>
>> 3. Replace pgd_populate with p4d_populate, it will be useful if there
>> four-level page tables.
>>
>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>> ---
>>  arch/loongarch/kernel/numa.c | 33 ++++++++++++++++++++-------------
>>  1 file changed, 20 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
>> index 708665895b47..778e1c20bfb0 100644
>> --- a/arch/loongarch/kernel/numa.c
>> +++ b/arch/loongarch/kernel/numa.c
>> @@ -73,33 +73,40 @@ void __init pcpu_populate_pte(unsigned long addr)
>>         pmd_t *pmd;
>>
>>         if (p4d_none(*p4d)) {
>> -               pud_t *new;
>> -
>> -               new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>> -               pgd_populate(&init_mm, pgd, new);
>> +               pud = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
> Don't use memblock_alloc_raw() here, it is better to keep consistency
> with mm/percpu.c.
memblock_alloc will clear the page, and there will be page table initialization
with the following pud_init(pud). memblock_alloc_raw will not clear the page.

I prefer memblock_alloc_raw for better performance however ok with both, it is
up to you to decide.

Regards
Bibo Mao

> 
> 
> Huacai
>> +               if (!pud)
>> +                       goto err_alloc;
>> +               p4d_populate(&init_mm, p4d, pud);
>>  #ifndef __PAGETABLE_PUD_FOLDED
>> -               pud_init(new);
>> +               pud_init(pud);
>>  #endif
>>         }
>>
>>         pud = pud_offset(p4d, addr);
>>         if (pud_none(*pud)) {
>> -               pmd_t *new;
>> -
>> -               new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>> -               pud_populate(&init_mm, pud, new);
>> +               pmd = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
>> +               if (!pmd)
>> +                       goto err_alloc;
>> +               pud_populate(&init_mm, pud, pmd);
>>  #ifndef __PAGETABLE_PMD_FOLDED
>> -               pmd_init(new);
>> +               pmd_init(pmd);
>>  #endif
>>         }
>>
>>         pmd = pmd_offset(pud, addr);
>>         if (!pmd_present(*pmd)) {
>> -               pte_t *new;
>> +               pte_t *pte;
>>
>> -               new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>> -               pmd_populate_kernel(&init_mm, pmd, new);
>> +               pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>> +               if (!pte)
>> +                       goto err_alloc;
>> +               pmd_populate_kernel(&init_mm, pmd, pte);
>>         }
>> +
>> +       return;
>> +
>> +err_alloc:
>> +       panic("%s: Failed to allocate memory\n", __func__);
>>  }
>>
>>  void __init setup_per_cpu_areas(void)
>> --
>> 2.27.0
>>