Re: [PATCH v2 08/46] hugetlb: add HugeTLB HGM enablement helpers

[James Houghton]

On Fri, Feb 17, 2023 at 5:40 PM Mina Almasry <almasrymina@xxxxxxxxxx> wrote:
>
> On Fri, Feb 17, 2023 at 4:28 PM James Houghton <jthoughton@xxxxxxxxxx> wrote:
> >
> > hugetlb_hgm_eligible indicates that a VMA is eligible to have HGM
> > explicitly enabled via MADV_SPLIT, and hugetlb_hgm_enabled indicates
> > that HGM has been enabled.
> >
> > Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
>
> Only nits:
> Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>

Thanks Mina. :)

>
> >
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 7c977d234aba..efd2635a87f5 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -1211,6 +1211,20 @@ static inline void hugetlb_unregister_node(struct node *node)
> >  }
> >  #endif /* CONFIG_HUGETLB_PAGE */
> >
> > +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> > +bool hugetlb_hgm_enabled(struct vm_area_struct *vma);
> > +bool hugetlb_hgm_eligible(struct vm_area_struct *vma);
> > +#else
> > +static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> > +{
> > +       return false;
> > +}
> > +static inline bool hugetlb_hgm_eligible(struct vm_area_struct *vma)
> > +{
> > +       return false;
> > +}
> > +#endif
> > +
> >  static inline spinlock_t *huge_pte_lock(struct hstate *h,
> >                                         struct mm_struct *mm, pte_t *pte)
> >  {
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 6c008c9de80e..0576dcc98044 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -7004,6 +7004,10 @@ static bool pmd_sharing_possible(struct vm_area_struct *vma)
> >  #ifdef CONFIG_USERFAULTFD
> >         if (uffd_disable_huge_pmd_share(vma))
> >                 return false;
> > +#endif
> > +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> > +       if (hugetlb_hgm_enabled(vma))
> > +               return false;
> >  #endif
> >         /*
> >          * Only shared VMAs can share PMDs.
> > @@ -7267,6 +7271,18 @@ __weak unsigned long hugetlb_mask_last_page(struct hstate *h)
> >
> >  #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
> >
> > +#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> > +bool hugetlb_hgm_eligible(struct vm_area_struct *vma)
>
> I think the other function you named pmd_sharing_possible(), I suggest
> hugetlb_hgm_possible() for some consistency.

Good idea. Will do.

>
> > +{
> > +       /* All shared VMAs may have HGM. */
>
> I think this is a redundant comment.

Indeed. I'll change it to something like:

"HGM is not supported for private mappings. Operations that apply to
MAP_PRIVATE VMAs like hugetlb_wp haven't been updated to support
high-granularity mappings."

>
> > +       return vma && (vma->vm_flags & VM_MAYSHARE);
> > +}
> > +bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
> > +{
> > +       return vma && (vma->vm_flags & VM_HUGETLB_HGM);
> > +}
> > +#endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
> > +
> >  /*
> >   * These functions are overwritable if your architecture needs its own
> >   * behavior.
> > --
> > 2.39.2.637.g21b0678d19-goog
> >