linux-kernel - Re: [PATCH v8 02/15] introduce khugepaged_collapse_single_pmd to unify khugepaged and madvise

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Message-ID: <CAA1CXcDH5xTSGHJu13Gb3EfNnntKwQn6Oq6rhS5uFoyLwid0Jw@mail.gmail.com>
Date: Thu, 3 Jul 2025 22:20:01 -0600
From: Nico Pache <npache@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v8 02/15] introduce khugepaged_collapse_single_pmd to
 unify khugepaged and madvise_collapse

On Thu, Jul 3, 2025 at 9:51 PM Baolin Wang
<baolin.wang@...ux.alibaba.com> wrote:
>
>
>
> On 2025/7/2 13:57, Nico Pache wrote:
> > The khugepaged daemon and madvise_collapse have two different
> > implementations that do almost the same thing.
> >
> > Create khugepaged_collapse_single_pmd to increase code reuse and create an
> > entry point these two users.
> >
> > Refactor madvise_collapse and khugepaged_scan_mm_slot to use the new
> > khugepaged_collapse_single_pmd function. This introduces a minor
> > behavioral change that is most likely an undiscovered bug. The current
> > implementation of khugepaged tests khugepaged_test_exit_or_disable
> > before calling khugepaged_pte_mapped_thp, but we weren't doing it in the
> > madvise_collapse case. By unifying these two callers madvise_collapse
> > now also performs this check.
> >
> > Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> > Signed-off-by: Nico Pache <npache@...hat.com>
> > ---
> >   mm/khugepaged.c | 95 +++++++++++++++++++++++++------------------------
> >   1 file changed, 49 insertions(+), 46 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index f27fe7ca9b86..bf69e81a3d82 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -2354,6 +2354,50 @@ static int khugepaged_scan_file(struct mm_struct *mm, unsigned long addr,
> >       return result;
> >   }
> >
> > +/*
> > + * Try to collapse a single PMD starting at a PMD aligned addr, and return
> > + * the results.
> > + */
> > +static int khugepaged_collapse_single_pmd(unsigned long addr,
> > +                                struct vm_area_struct *vma, bool *mmap_locked,
> > +                                struct collapse_control *cc)
> > +{
> > +     int result = SCAN_FAIL;
> > +     struct mm_struct *mm = vma->vm_mm;
> > +
> > +     if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
>
> Seems you still forgot to drop 'IS_ENABLED(CONFIG_SHMEM)' :)
Hi Baolin,

You had me questioning my sanity for a moment because I SWEAR I did do
this! but now I see the issue, I accidentally merged the fixup into
patch 6 (not entirely sure how or why I would have done that given my
notes say it belongs in this patch...)

I'm sorry about that :< I'll see if I can work with Andrew to get some
fixups into mm-new (this was merged a few hours ago) for this patch
and patch 6.
>