Re: [PATCH v3 2/3] mm/rmap: integrate PMD-mapped folio splitting into pagewalk loop

[Lance Yang <ioworker0@gmail.com>]

On Tue, Apr 30, 2024 at 10:03 AM Lance Yang <ioworker0@gmail.com> wrote:
>
> Hey SJ,
>
> Thanks a lot for reporting!
>
> On Tue, Apr 30, 2024 at 4:20 AM SeongJae Park <sj@kernel.org> wrote:
> >
> > Hi Lance,
> >
> > On Mon, 29 Apr 2024 21:23:07 +0800 Lance Yang <ioworker0@gmail.com> wrote:
> >
> > > In preparation for supporting try_to_unmap_one() to unmap PMD-mapped
> > > folios, start the pagewalk first, then call split_huge_pmd_address()
> > > to split the folio.
> > >
> > > Suggested-by: David Hildenbrand <david@redhat.com>
> > > Signed-off-by: Lance Yang <ioworker0@gmail.com>
> > > ---
> > >  include/linux/huge_mm.h |  2 ++
> > >  mm/huge_memory.c        | 42 +++++++++++++++++++++--------------------
> > >  mm/rmap.c               | 26 +++++++++++++++++++------
> > >  3 files changed, 44 insertions(+), 26 deletions(-)
> > >
> > [...]
> > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > index 7e2575d669a9..e42f436c7ff3 100644
> > > --- a/mm/rmap.c
> > > +++ b/mm/rmap.c
> > > @@ -1636,9 +1636,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> > >       if (flags & TTU_SYNC)
> > >               pvmw.flags = PVMW_SYNC;
> > >
> > > -     if (flags & TTU_SPLIT_HUGE_PMD)
> > > -             split_huge_pmd_address(vma, address, false, folio);
> > > -
> > >       /*
> > >        * For THP, we have to assume the worse case ie pmd for invalidation.
> > >        * For hugetlb, it could be much worse if we need to do pud
> > > @@ -1650,6 +1647,10 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> > >       range.end = vma_address_end(&pvmw);
> > >       mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
> > >                               address, range.end);
> > > +     if (flags & TTU_SPLIT_HUGE_PMD) {
> > > +             range.start = address & HPAGE_PMD_MASK;
> > > +             range.end = (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE;
> > > +     }
> >
> > I found the latest mm-unstable fails one[1] of my build configuration
> > with below error message.  And 'git bisect' points this patch.
>
> Thanks for taking time to 'git bisect' and identify this bug!
>
> >
> >       CC      mm/rmap.o
> >     In file included from <command-line>:
> >     .../linux/mm/rmap.c: In function 'try_to_unmap_one':
> >     .../linux/include/linux/compiler_types.h:460:38: error: call to '__compiletime_assert_455' declared with attribute error: BUILD_BUG failed
> >       460 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> >           |                                      ^
> >     .../linux/include/linux/compiler_types.h:441:4: note: in definition of macro '__compiletime_assert'
> >       441 |    prefix ## suffix();    \
> >           |    ^~~~~~
> >     .../linux/include/linux/compiler_types.h:460:2: note: in expansion of macro '_compiletime_assert'
> >       460 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> >           |  ^~~~~~~~~~~~~~~~~~~
> >     .../linux/include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
> >        39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> >           |                                     ^~~~~~~~~~~~~~~~~~
> >     .../linux/include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> >        59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
> >           |                     ^~~~~~~~~~~~~~~~
> >     .../linux/include/linux/huge_mm.h:97:28: note: in expansion of macro 'BUILD_BUG'
> >        97 | #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> >           |                            ^~~~~~~~~
> >     .../linux/include/linux/huge_mm.h:104:34: note: in expansion of macro 'HPAGE_PMD_SHIFT'
> >       104 | #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT)
> >           |                                  ^~~~~~~~~~~~~~~
> >     .../linux/include/linux/huge_mm.h:103:27: note: in expansion of macro 'HPAGE_PMD_SIZE'
> >       103 | #define HPAGE_PMD_MASK (~(HPAGE_PMD_SIZE - 1))
> >           |                           ^~~~~~~~~~~~~~
> >     .../linux/mm/rmap.c:1651:27: note: in expansion of macro 'HPAGE_PMD_MASK'
> >      1651 |   range.start = address & HPAGE_PMD_MASK;
> >           |                           ^~~~~~~~~~~~~~
> >
> > I haven't looked into the code yet, but seems this code need to handle
> > CONFIG_PGTABLE_HAS_HUGE_LEAVES undefined case?  May I ask your opinion?
> >
> > [1] https://github.com/awslabs/damon-tests/blob/next/corr/tests/build_arm64.sh
>
> I'll fix this bug and rebuild using the config you've provided above.

Hey Andrew,

Could you please temporarily drop this series from the mm tree?
I'll fix this bug in the next version.

Thanks,
Lance

>
> Thanks again for reporting!
> Lance
>
> >
> >
> > Thanks,
> > SJ
> > [...]