Re: [mm-unstable v7 07/18] mm/thp: add flag to enforce sysfs THP in hugepage_vma_check()

[Zach O'Keefe <zokeefe@google.com>]

On Jul 11 13:57, Yang Shi wrote:
> On Wed, Jul 6, 2022 at 5:06 PM Zach O'Keefe <zokeefe@google.com> wrote:
> >
> > MADV_COLLAPSE is not coupled to the kernel-oriented sysfs THP settings[1].
> >
> > hugepage_vma_check() is the authority on determining if a VMA is eligible
> > for THP allocation/collapse, and currently enforces the sysfs THP settings.
> > Add a flag to disable these checks.  For now, only apply this arg to anon
> > and file, which use /sys/kernel/transparent_hugepage/enabled.  We can
> > expand this to shmem, which uses
> > /sys/kernel/transparent_hugepage/shmem_enabled, later.
> >
> > Use this flag in collapse_pte_mapped_thp() where previously the VMA flags
> > passed to hugepage_vma_check() were OR'd with VM_HUGEPAGE to elide the
> > VM_HUGEPAGE check in "madvise" THP mode. Prior to "mm: khugepaged: check
> > THP flag in hugepage_vma_check()", this check also didn't check "never" THP
> > mode.  As such, this restores the previous behavior of
> > collapse_pte_mapped_thp() where sysfs THP settings are ignored.  See
> > comment in code for justification why this is OK.
> >
> > [1] https://lore.kernel.org/linux-mm/CAAa6QmQxay1_=Pmt8oCX2-Va18t44FV-Vs-WsQt_6+qBks4nZA@mail.gmail.com/
> >
> > Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> 
> Reviewed-by: Yang Shi <shy828301@gmail.com>

Thanks for the review!

Best,
Zach

> > ---
> >  fs/proc/task_mmu.c      |  2 +-
> >  include/linux/huge_mm.h |  9 ++++-----
> >  mm/huge_memory.c        | 14 ++++++--------
> >  mm/khugepaged.c         | 25 ++++++++++++++-----------
> >  mm/memory.c             |  4 ++--
> >  5 files changed, 27 insertions(+), 27 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 34d292cec79a..f8cd58846a28 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -866,7 +866,7 @@ static int show_smap(struct seq_file *m, void *v)
> >         __show_smap(m, &mss, false);
> >
> >         seq_printf(m, "THPeligible:    %d\n",
> > -                  hugepage_vma_check(vma, vma->vm_flags, true, false));
> > +                  hugepage_vma_check(vma, vma->vm_flags, true, false, true));
> >
> >         if (arch_pkeys_enabled())
> >                 seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 37f2f11a6d7e..00312fc251c1 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -168,9 +168,8 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
> >                !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
> >  }
> >
> > -bool hugepage_vma_check(struct vm_area_struct *vma,
> > -                       unsigned long vm_flags,
> > -                       bool smaps, bool in_pf);
> > +bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
> > +                       bool smaps, bool in_pf, bool enforce_sysfs);
> >
> >  #define transparent_hugepage_use_zero_page()                           \
> >         (transparent_hugepage_flags &                                   \
> > @@ -321,8 +320,8 @@ static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
> >  }
> >
> >  static inline bool hugepage_vma_check(struct vm_area_struct *vma,
> > -                                      unsigned long vm_flags,
> > -                                      bool smaps, bool in_pf)
> > +                                     unsigned long vm_flags, bool smaps,
> > +                                     bool in_pf, bool enforce_sysfs)
> >  {
> >         return false;
> >  }
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index da300ce9dedb..4fbe43dc1568 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -69,9 +69,8 @@ static atomic_t huge_zero_refcount;
> >  struct page *huge_zero_page __read_mostly;
> >  unsigned long huge_zero_pfn __read_mostly = ~0UL;
> >
> > -bool hugepage_vma_check(struct vm_area_struct *vma,
> > -                       unsigned long vm_flags,
> > -                       bool smaps, bool in_pf)
> > +bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
> > +                       bool smaps, bool in_pf, bool enforce_sysfs)
> >  {
> >         if (!vma->vm_mm)                /* vdso */
> >                 return false;
> > @@ -120,11 +119,10 @@ bool hugepage_vma_check(struct vm_area_struct *vma,
> >         if (!in_pf && shmem_file(vma->vm_file))
> >                 return shmem_huge_enabled(vma);
> >
> > -       if (!hugepage_flags_enabled())
> > -               return false;
> > -
> > -       /* THP settings require madvise. */
> > -       if (!(vm_flags & VM_HUGEPAGE) && !hugepage_flags_always())
> > +       /* Enforce sysfs THP requirements as necessary */
> > +       if (enforce_sysfs &&
> > +           (!hugepage_flags_enabled() || (!(vm_flags & VM_HUGEPAGE) &&
> > +                                          !hugepage_flags_always())))
> >                 return false;
> >
> >         /* Only regular file is valid */
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index d89056d8cbad..b0e20db3f805 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -478,7 +478,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
> >  {
> >         if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
> >             hugepage_flags_enabled()) {
> > -               if (hugepage_vma_check(vma, vm_flags, false, false))
> > +               if (hugepage_vma_check(vma, vm_flags, false, false, true))
> >                         __khugepaged_enter(vma->vm_mm);
> >         }
> >  }
> > @@ -844,7 +844,8 @@ static bool khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
> >   */
> >
> >  static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> > -               struct vm_area_struct **vmap)
> > +                                  struct vm_area_struct **vmap,
> > +                                  struct collapse_control *cc)
> >  {
> >         struct vm_area_struct *vma;
> >
> > @@ -855,7 +856,8 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> >         if (!vma)
> >                 return SCAN_VMA_NULL;
> >
> > -       if (!hugepage_vma_check(vma, vma->vm_flags, false, false))
> > +       if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
> > +                               cc->is_khugepaged))
> >                 return SCAN_VMA_CHECK;
> >         /*
> >          * Anon VMA expected, the address may be unmapped then
> > @@ -974,7 +976,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> >                 goto out_nolock;
> >
> >         mmap_read_lock(mm);
> > -       result = hugepage_vma_revalidate(mm, address, &vma);
> > +       result = hugepage_vma_revalidate(mm, address, &vma, cc);
> >         if (result != SCAN_SUCCEED) {
> >                 mmap_read_unlock(mm);
> >                 goto out_nolock;
> > @@ -1006,7 +1008,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> >          * handled by the anon_vma lock + PG_lock.
> >          */
> >         mmap_write_lock(mm);
> > -       result = hugepage_vma_revalidate(mm, address, &vma);
> > +       result = hugepage_vma_revalidate(mm, address, &vma, cc);
> >         if (result != SCAN_SUCCEED)
> >                 goto out_up_write;
> >         /* check if the pmd is still valid */
> > @@ -1350,12 +1352,13 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
> >                 return;
> >
> >         /*
> > -        * This vm_flags may not have VM_HUGEPAGE if the page was not
> > -        * collapsed by this mm. But we can still collapse if the page is
> > -        * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
> > -        * will not fail the vma for missing VM_HUGEPAGE
> > +        * If we are here, we've succeeded in replacing all the native pages
> > +        * in the page cache with a single hugepage. If a mm were to fault-in
> > +        * this memory (mapped by a suitably aligned VMA), we'd get the hugepage
> > +        * and map it by a PMD, regardless of sysfs THP settings. As such, let's
> > +        * analogously elide sysfs THP settings here.
> >          */
> > -       if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE, false, false))
> > +       if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
> >                 return;
> >
> >         /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
> > @@ -2042,7 +2045,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> >                         progress++;
> >                         break;
> >                 }
> > -               if (!hugepage_vma_check(vma, vma->vm_flags, false, false)) {
> > +               if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
> >  skip:
> >                         progress++;
> >                         continue;
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 8917bea2f0bc..96cd776e84f1 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5001,7 +5001,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> >                 return VM_FAULT_OOM;
> >  retry_pud:
> >         if (pud_none(*vmf.pud) &&
> > -           hugepage_vma_check(vma, vm_flags, false, true)) {
> > +           hugepage_vma_check(vma, vm_flags, false, true, true)) {
> >                 ret = create_huge_pud(&vmf);
> >                 if (!(ret & VM_FAULT_FALLBACK))
> >                         return ret;
> > @@ -5035,7 +5035,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> >                 goto retry_pud;
> >
> >         if (pmd_none(*vmf.pmd) &&
> > -           hugepage_vma_check(vma, vm_flags, false, true)) {
> > +           hugepage_vma_check(vma, vm_flags, false, true, true)) {
> >                 ret = create_huge_pmd(&vmf);
> >                 if (!(ret & VM_FAULT_FALLBACK))
> >                         return ret;
> > --
> > 2.37.0.rc0.161.g10f37bed90-goog
> >
> >