linux-kernel - Re: [PATCH 2/7] mm: thp: introduce transhuge_vma_size

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Date:   Mon, 23 May 2022 11:12:18 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/7] mm: thp: introduce transhuge_vma_size_ok() helper

On Fri, May 20, 2022 at 6:40 PM Hillf Danton <hdanton@...a.com> wrote:
>
> On Fri, 20 May 2022 14:16:00 -0700 Yang Shi wrote:
> > There are couple of places that check whether the vma size is ok for
> > THP or not, they are open coded and duplicate, introduce
> > transhuge_vma_size_ok() helper to do the job.
> >
> > Signed-off-by: Yang Shi <shy828301@...il.com>
> > ---
> >  include/linux/huge_mm.h | 17 +++++++++++++++++
> >  mm/huge_memory.c        |  5 +----
> >  mm/khugepaged.c         | 12 ++++++------
> >  3 files changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 648cb3ce7099..a8f61db47f2a 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -116,6 +116,18 @@ extern struct kobj_attribute shmem_enabled_attr;
> >
> >  extern unsigned long transparent_hugepage_flags;
> >
> > +/*
> > + * The vma size has to be large enough to hold an aligned HPAGE_PMD_SIZE area.
> > + */
> > +static inline bool transhuge_vma_size_ok(struct vm_area_struct *vma)
> > +{
> > +     if (round_up(vma->vm_start, HPAGE_PMD_SIZE) <
> > +         (vma->vm_end & HPAGE_PMD_MASK))
> > +             return true;
> > +
> > +     return false;
> > +}
> > +
> >  static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
> >               unsigned long addr)
> >  {
> > @@ -345,6 +357,11 @@ static inline bool transparent_hugepage_active(struct vm_area_struct *vma)
> >       return false;
> >  }
> >
> > +static inline bool transhuge_vma_size_ok(struct vm_area_struct *vma)
> > +{
> > +     return false;
> > +}
> > +
> >  static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
> >               unsigned long addr)
> >  {
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 80e8b58b4f39..d633f97452c1 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -71,10 +71,7 @@ unsigned long huge_zero_pfn __read_mostly = ~0UL;
> >
> >  bool transparent_hugepage_active(struct vm_area_struct *vma)
> >  {
> > -     /* The addr is used to check if the vma size fits */
> > -     unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;
> > -
> > -     if (!transhuge_vma_suitable(vma, addr))
> > +     if (!transhuge_vma_size_ok(vma))
> >               return false;
>
> Given the comment added in 4/7, this patch adds change in semantic.
> If that is intened, add some words in log message for it.

It should not change the semantic even with 4/7. The old comment says
"The addr is used to check if the vma size fits", so the purpose of
transhuge_vma_suitable() here is used to check if the vma size is ok
or not.

>
> >       if (vma_is_anonymous(vma))
> >               return __transparent_hugepage_enabled(vma);
>