Re: [PATCH V5 3/4] mm/sparse-vmemmap: Generalise vmemmap_populate_hugepages()

[Huacai Chen <chenhuacai@kernel.org>]

Hi, Will,

On Fri, Jul 22, 2022 at 5:16 PM Will Deacon <will@kernel.org> wrote:
>
> On Thu, Jul 21, 2022 at 09:04:18PM +0800, Huacai Chen wrote:
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index 0abcb0a5f1b5..eafd084b8e19 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -694,6 +694,69 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
> >       return vmemmap_populate_range(start, end, node, altmap, NULL);
> >  }
> >
> > +void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> > +                                   unsigned long addr, unsigned long next)
> > +{
> > +}
> > +
> > +int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node, unsigned long addr,
> > +                                    unsigned long next)
> > +{
> > +     return 0;
> > +}
> > +
> > +int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
> > +                                      int node, struct vmem_altmap *altmap)
> > +{
> > +     unsigned long addr;
> > +     unsigned long next;
> > +     pgd_t *pgd;
> > +     p4d_t *p4d;
> > +     pud_t *pud;
> > +     pmd_t *pmd;
> > +
> > +     for (addr = start; addr < end; addr = next) {
> > +             next = pmd_addr_end(addr, end);
> > +
> > +             pgd = vmemmap_pgd_populate(addr, node);
> > +             if (!pgd)
> > +                     return -ENOMEM;
> > +
> > +             p4d = vmemmap_p4d_populate(pgd, addr, node);
> > +             if (!p4d)
> > +                     return -ENOMEM;
> > +
> > +             pud = vmemmap_pud_populate(p4d, addr, node);
> > +             if (!pud)
> > +                     return -ENOMEM;
> > +
> > +             pmd = pmd_offset(pud, addr);
> > +             if (pmd_none(READ_ONCE(*pmd))) {
> > +                     void *p;
> > +
> > +                     p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
> > +                     if (p) {
> > +                             vmemmap_set_pmd(pmd, p, node, addr, next);
> > +                             continue;
> > +                     } else if (altmap) {
> > +                             /*
> > +                              * No fallback: In any case we care about, the
> > +                              * altmap should be reasonably sized and aligned
> > +                              * such that vmemmap_alloc_block_buf() will always
> > +                              * succeed. If there is no more space in the altmap
> > +                              * and we'd have to fallback to PTE (highly unlikely).
>
> Can you tweak the last couple of sentences please, as they don't make sense
> to me? To be specific, I'd suggest replacing:
>
>   "If there is no more space in the altmap and we'd have to fallback to PTE
>   (highly unlikely). That could indicate an altmap-size configuration
>   issue."
>
> with something like:
>
>   "For consistency with the PTE case, return an error here as failure could
>    indicate a configuration issue with the size of the altmap."
>
> With that:
>
> Acked-by: Will Deacon <will@kernel.org>
OK, I will send V5, thanks.

Huacai
>
> Will