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Date: Thu, 10 Aug 2023 12:27:11 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: bibo mao <maobibo@...ngson.cn>
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 3/3] LoongArch: mm: Add unified function populate_kernel_pte
On Thu, Aug 10, 2023 at 12:09 PM bibo mao <maobibo@...ngson.cn> wrote:
>
>
>
> 在 2023/8/2 15:25, Huacai Chen 写道:
> > On Tue, Aug 1, 2023 at 9:22 AM bibo mao <maobibo@...ngson.cn> wrote:
> >>
> >>
> >>
> >> 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:
> >>>>
> >>>> Function pcpu_populate_pte and fixmap_pte are similar, they populate
> >>>> one page from kernel address space. And there is confusion between
> >>>> pgd and p4d in function fixmap_pte, such as pgd_none always returns
> >>>> zero. This patch adds unified function populate_kernel_pte and replaces
> >>>> pcpu_populate_pte and fixmap_pte.
> >>>>
> >>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> >>>> ---
> >>>> arch/loongarch/include/asm/pgalloc.h | 1 +
> >>>> arch/loongarch/kernel/numa.c | 40 +--------------------
> >>>> arch/loongarch/mm/init.c | 52 ++++++++++++++++------------
> >>>> 3 files changed, 32 insertions(+), 61 deletions(-)
> >>>>
> >>>> diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
> >>>> index af1d1e4a6965..ca17b573dba6 100644
> >>>> --- a/arch/loongarch/include/asm/pgalloc.h
> >>>> +++ b/arch/loongarch/include/asm/pgalloc.h
> >>>> @@ -91,4 +91,5 @@ static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long address)
> >>>>
> >>>> #endif /* __PAGETABLE_PUD_FOLDED */
> >>>>
> >>>> +extern pte_t * __init populate_kernel_pte(unsigned long addr);
> >>>> #endif /* _ASM_PGALLOC_H */
> >>>> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
> >>>> index 778e1c20bfb0..24a693b76873 100644
> >>>> --- a/arch/loongarch/kernel/numa.c
> >>>> +++ b/arch/loongarch/kernel/numa.c
> >>>> @@ -67,46 +67,8 @@ static int __init pcpu_cpu_distance(unsigned int from, unsigned int to)
> >>>>
> >>>> void __init pcpu_populate_pte(unsigned long addr)
> >>>> {
> >>>> - pgd_t *pgd = pgd_offset_k(addr);
> >>>> - p4d_t *p4d = p4d_offset(pgd, addr);
> >>>> - pud_t *pud;
> >>>> - pmd_t *pmd;
> >>>> -
> >>>> - if (p4d_none(*p4d)) {
> >>>> - pud = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
> >>>> - if (!pud)
> >>>> - goto err_alloc;
> >>>> - p4d_populate(&init_mm, p4d, pud);
> >>>> -#ifndef __PAGETABLE_PUD_FOLDED
> >>>> - pud_init(pud);
> >>>> -#endif
> >>>> - }
> >>>> -
> >>>> - pud = pud_offset(p4d, addr);
> >>>> - if (pud_none(*pud)) {
> >>>> - 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(pmd);
> >>>> -#endif
> >>>> - }
> >>>> -
> >>>> - pmd = pmd_offset(pud, addr);
> >>>> - if (!pmd_present(*pmd)) {
> >>>> - pte_t *pte;
> >>>> -
> >>>> - pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> >>>> - if (!pte)
> >>>> - goto err_alloc;
> >>>> - pmd_populate_kernel(&init_mm, pmd, pte);
> >>>> - }
> >>>> -
> >>>> + populate_kernel_pte(addr);
> >>>> return;
> >>>> -
> >>>> -err_alloc:
> >>>> - panic("%s: Failed to allocate memory\n", __func__);
> >>>> }
> >>>>
> >>>> void __init setup_per_cpu_areas(void)
> >>>> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> >>>> index 3b7d8129570b..6cd2948373ae 100644
> >>>> --- a/arch/loongarch/mm/init.c
> >>>> +++ b/arch/loongarch/mm/init.c
> >>>> @@ -191,46 +191,49 @@ void vmemmap_free(unsigned long start, unsigned long end, struct vmem_altmap *al
> >>>> #endif
> >>>> #endif
> >>>>
> >>>> -static pte_t *fixmap_pte(unsigned long addr)
> >>>> +pte_t * __init populate_kernel_pte(unsigned long addr)
> >>>> {
> >>>> - pgd_t *pgd;
> >>>> - p4d_t *p4d;
> >>>> + pgd_t *pgd = pgd_offset_k(addr);
> >>>> + p4d_t *p4d = p4d_offset(pgd, addr);
> >>>> pud_t *pud;
> >>>> pmd_t *pmd;
> >>>>
> >>>> - pgd = pgd_offset_k(addr);
> >>>> - p4d = p4d_offset(pgd, addr);
> >>>> -
> >>>> - if (pgd_none(*pgd)) {
> >>>> - pud_t *new __maybe_unused;
> >>>> -
> >>>> - new = memblock_alloc_low(PAGE_SIZE, PAGE_SIZE);
> >>>> - pgd_populate(&init_mm, pgd, new);
> >>>> + if (p4d_none(*p4d)) {
> >>>> + pud = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
> >>>> + 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 __maybe_unused;
> >>>> -
> >>>> - new = memblock_alloc_low(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_none(*pmd)) {
> >>>> - pte_t *new __maybe_unused;
> >>>> + if (!pmd_present(*pmd)) {
> >>>> + pte_t *pte;
> >>>>
> >>>> - new = memblock_alloc_low(PAGE_SIZE, PAGE_SIZE);
> >>>> - pmd_populate_kernel(&init_mm, pmd, new);
> >>>> + pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> >>> I don't think memblock_alloc_low() here can be replaced by memblock_alloc().
> >> Can you share me the points that pte table must be allocated with memblock_alloc_low
> >> in this place?
> > I forget the reason now, so if you confirm memblock_alloc() works well
> > here, you can use it. But please don't use memblock_alloc_raw().
> what a mess, there is more comments if there is special reason, else everyone can
> forgot by elapsed time.
>
> why the function memblock_alloc_raw can not be use? there is one useless page copy.
This is not a performance critical path, keeping consistency with
mm/percpu.c can make life easier.
Huacai
>
> Regards
> Bibo Mao
>
>
> >
> > Huacai
> >>
> >> Regards
> >> Bibo Mao
> >>>
> >>>
> >>> Huacai
> >>>> + if (!pte)
> >>>> + goto err_alloc;
> >>>> + pmd_populate_kernel(&init_mm, pmd, pte);
> >>>> }
> >>>>
> >>>> return pte_offset_kernel(pmd, addr);
> >>>> +
> >>>> +err_alloc:
> >>>> + panic("%s: Failed to allocate memory\n", __func__);
> >>>> + return NULL;
> >>>> }
> >>>>
> >>>> void __init __set_fixmap(enum fixed_addresses idx,
> >>>> @@ -241,7 +244,12 @@ void __init __set_fixmap(enum fixed_addresses idx,
> >>>>
> >>>> BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
> >>>>
> >>>> - ptep = fixmap_pte(addr);
> >>>> + /*
> >>>> + * Now only FIX_EARLYCON_MEM_BASE fixed map is used
> >>>> + * __set_fixmap must be called before mem_init since function
> >>>> + * populate_kernel_pte allocates memory with memblock_alloc method.
> >>>> + */
> >>>> + ptep = populate_kernel_pte(addr);
> >>>> if (!pte_none(*ptep)) {
> >>>> pte_ERROR(*ptep);
> >>>> return;
> >>>> --
> >>>> 2.27.0
> >>>>
> >>
> >>
>
>
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