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Date: Tue, 14 Jun 2022 12:16:36 -0700
From: Yang Shi <shy828301@...il.com>
To: "Zach O'Keefe" <zokeefe@...gle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux MM <linux-mm@...ck.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v3 PATCH 5/7] mm: thp: kill transparent_hugepage_active()
On Mon, Jun 13, 2022 at 8:06 AM Zach O'Keefe <zokeefe@...gle.com> wrote:
>
> On 10 Jun 10:02, Yang Shi wrote:
> > On Thu, Jun 9, 2022 at 6:03 PM Zach O'Keefe <zokeefe@...gle.com> wrote:
> > >
> > > On Mon, Jun 6, 2022 at 2:44 PM Yang Shi <shy828301@...il.com> wrote:
> > > >
> > > > The transparent_hugepage_active() was introduced to show THP eligibility
> > > > bit in smaps in proc, smaps is the only user. But it actually does the
> > > > similar check as hugepage_vma_check() which is used by khugepaged. We
> > > > definitely don't have to maintain two similar checks, so kill
> > > > transparent_hugepage_active().
> > >
> > > I never realized smaps was the only user! Great!
> > >
> > > > Also move hugepage_vma_check() to huge_memory.c and huge_mm.h since it
> > > > is not only for khugepaged anymore.
> > > >
> > > > Signed-off-by: Yang Shi <shy828301@...il.com>
> > > > ---
> > > > fs/proc/task_mmu.c | 2 +-
> > > > include/linux/huge_mm.h | 16 +++++++-----
> > > > include/linux/khugepaged.h | 4 +--
> > > > mm/huge_memory.c | 50 ++++++++++++++++++++++++++++++++-----
> > > > mm/khugepaged.c | 51 +++-----------------------------------
> > > > 5 files changed, 60 insertions(+), 63 deletions(-)
> > > >
> > > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > > > index 2dd8c8a66924..fd79566e204c 100644
> > > > --- a/fs/proc/task_mmu.c
> > > > +++ b/fs/proc/task_mmu.c
> > > > @@ -860,7 +860,7 @@ static int show_smap(struct seq_file *m, void *v)
> > > > __show_smap(m, &mss, false);
> > > >
> > > > seq_printf(m, "THPeligible: %d\n",
> > > > - transparent_hugepage_active(vma));
> > > > + hugepage_vma_check(vma, vma->vm_flags, 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 79d5919beb83..f561c3e16def 100644
> > > > --- a/include/linux/huge_mm.h
> > > > +++ b/include/linux/huge_mm.h
> > > > @@ -209,7 +209,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
> > > > !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
> > > > }
> > > >
> > > > -bool transparent_hugepage_active(struct vm_area_struct *vma);
> > > > +bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > + unsigned long vm_flags,
> > > > + bool smaps);
> > > >
> > > > #define transparent_hugepage_use_zero_page() \
> > > > (transparent_hugepage_flags & \
> > > > @@ -358,11 +360,6 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
> > > > return false;
> > > > }
> > > >
> > > > -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;
> > > > @@ -380,6 +377,13 @@ static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
> > > > return false;
> > > > }
> > > >
> > > > +static inline bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > + unsigned long vm_flags,
> > > > + bool smaps)
> > > > +{
> > > > + return false;
> > > > +}
> > > > +
> > > > static inline void prep_transhuge_page(struct page *page) {}
> > > >
> > > > #define transparent_hugepage_flags 0UL
> > > > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> > > > index 392d34c3c59a..8a6452e089ca 100644
> > > > --- a/include/linux/khugepaged.h
> > > > +++ b/include/linux/khugepaged.h
> > > > @@ -10,8 +10,6 @@ extern struct attribute_group khugepaged_attr_group;
> > > > extern int khugepaged_init(void);
> > > > extern void khugepaged_destroy(void);
> > > > extern int start_stop_khugepaged(void);
> > > > -extern bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > - unsigned long vm_flags);
> > > > extern void __khugepaged_enter(struct mm_struct *mm);
> > > > extern void __khugepaged_exit(struct mm_struct *mm);
> > > > extern void khugepaged_enter_vma(struct vm_area_struct *vma,
> > > > @@ -57,7 +55,7 @@ static inline void khugepaged_enter(struct vm_area_struct *vma,
> > > > {
> > > > if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
> > > > khugepaged_enabled()) {
> > > > - if (hugepage_vma_check(vma, vm_flags))
> > > > + if (hugepage_vma_check(vma, vm_flags, false))
> > > > __khugepaged_enter(vma->vm_mm);
> > > > }
> > > > }
> > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > > index 36ada544e494..bc8370856e85 100644
> > > > --- a/mm/huge_memory.c
> > > > +++ b/mm/huge_memory.c
> > > > @@ -69,18 +69,56 @@ static atomic_t huge_zero_refcount;
> > > > struct page *huge_zero_page __read_mostly;
> > > > unsigned long huge_zero_pfn __read_mostly = ~0UL;
> > > >
> > > > -bool transparent_hugepage_active(struct vm_area_struct *vma)
> > > > +bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > + unsigned long vm_flags,
> > > > + bool smaps)
> > > > {
> > > > + if (!transhuge_vma_enabled(vma, vm_flags))
> > > > + return false;
> > > > +
> > > > + if (vm_flags & VM_NO_KHUGEPAGED)
> > > > + return false;
> > > > +
> > > > + /* Don't run khugepaged against DAX vma */
> > > > + if (vma_is_dax(vma))
> > > > + return false;
> > > > +
> > > > + if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> > > > + vma->vm_pgoff, HPAGE_PMD_NR))
> > > > + return false;
> > > > +
> > > > if (!transhuge_vma_size_ok(vma))
> > > > return false;
>
> I know we just introduced transhuge_vma_size_ok(), but is there a way to
> consolidate the above two checks into a single transhuge_vma_suitable(), the
> same way it used to be done in transparent_hugepage_active()? I.e.
>
> transhuge_vma_suitable(vma, vma->vm_end - HPAGE_PMD_SIZE).
>
> Which checks if the vma can hold an aligned hugepage, as well as centralizes
> the (what I think to be) complicated file mapping check.
Good point. Thanks for the suggestion. Actually
transhuge_vma_size_ok() is just called by hugepage_vma_check(). And
hugepage_vma_check() does check the alignment for file vma too, so I
think they could be consolidated into one function as you suggested.
And this should help keep the THPeligible bit the same throughout the
series.
>
> > > > - if (vma_is_anonymous(vma))
> > > > - return __transparent_hugepage_enabled(vma);
> > > > - if (vma_is_shmem(vma))
> > > > +
> > > > + /* Enabled via shmem mount options or sysfs settings. */
> > > > + if (shmem_file(vma->vm_file))
> > > > return shmem_huge_enabled(vma);
> > > > - if (transhuge_vma_enabled(vma, vma->vm_flags) && file_thp_enabled(vma))
> > > > +
> > > > + if (!khugepaged_enabled())
> > > > + return false;
> > > > +
> > > > + /* THP settings require madvise. */
> > > > + if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> > > > + return false;
> > > > +
> > > > + /* Only regular file is valid */
> > > > + if (file_thp_enabled(vma))
> > > > return true;
> > > >
> > > > - return false;
> > > > + if (!vma_is_anonymous(vma))
> > > > + return false;
> > > > +
> > > > + if (vma_is_temporary_stack(vma))
> > > > + return false;
> > > > +
> > > > + /*
> > > > + * THPeligible bit of smaps should show 1 for proper VMAs even
> > > > + * though anon_vma is not initialized yet.
> > > > + */
> > > > + if (!vma->anon_vma)
> > > > + return smaps;
> > > > +
> > > > + return true;
> > > > }
> > >
> > > There are a few cases where the return value for smaps will be
> > > different from before. I presume this won't be an issue, and that any
> > > difference resulting from this change is actually a positive
> > > difference, given it more accurately reflects the thp eligibility of
> > > the vma? For example, a VM_NO_KHUGEPAGED-marked vma might now show 0
> > > where it otherwise showed 1.
> >
> > Yes, returning 1 for VM_NO_KHUGEPAGED vmas is wrong. Actually TBH I
> > suspect very few people actually use this bit. Anyway I will elaborate
> > this in the commit log.
> >
> > >
> > > > static bool get_huge_zero_page(void)
> > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > > > index ca1754d3a827..aa0769e3b0d9 100644
> > > > --- a/mm/khugepaged.c
> > > > +++ b/mm/khugepaged.c
> > > > @@ -437,49 +437,6 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
> > > > return atomic_read(&mm->mm_users) == 0;
> > > > }
> > > >
> > > > -bool hugepage_vma_check(struct vm_area_struct *vma,
> > > > - unsigned long vm_flags)
> > > > -{
> > > > - if (!transhuge_vma_enabled(vma, vm_flags))
> > > > - return false;
> > > > -
> > > > - if (vm_flags & VM_NO_KHUGEPAGED)
> > > > - return false;
> > > > -
> > > > - /* Don't run khugepaged against DAX vma */
> > > > - if (vma_is_dax(vma))
> > > > - return false;
> > > > -
> > > > - if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> > > > - vma->vm_pgoff, HPAGE_PMD_NR))
> > > > - return false;
> > > > -
> > > > - if (!transhuge_vma_size_ok(vma))
> > > > - return false;
> > > > -
> > > > - /* Enabled via shmem mount options or sysfs settings. */
> > > > - if (shmem_file(vma->vm_file))
> > > > - return shmem_huge_enabled(vma);
> > > > -
> > > > - if (!khugepaged_enabled())
> > > > - return false;
> > > > -
> > > > - /* THP settings require madvise. */
> > > > - if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> > > > - return false;
> > > > -
> > > > - /* Only regular file is valid */
> > > > - if (file_thp_enabled(vma))
> > > > - return true;
> > > > -
> > > > - if (!vma->anon_vma || !vma_is_anonymous(vma))
> > > > - return false;
> > > > - if (vma_is_temporary_stack(vma))
> > > > - return false;
> > > > -
> > > > - return true;
> > > > -}
> > > > -
> > > > void __khugepaged_enter(struct mm_struct *mm)
> > > > {
> > > > struct mm_slot *mm_slot;
> > > > @@ -516,7 +473,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
> > > > {
> > > > if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
> > > > khugepaged_enabled()) {
> > > > - if (hugepage_vma_check(vma, vm_flags))
> > > > + if (hugepage_vma_check(vma, vm_flags, false))
> > > > __khugepaged_enter(vma->vm_mm);
> > > > }
> > > > }
> > > > @@ -961,7 +918,7 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> > > >
> > > > if (!transhuge_vma_suitable(vma, address))
> > > > return SCAN_ADDRESS_RANGE;
> > > > - if (!hugepage_vma_check(vma, vma->vm_flags))
> > > > + if (!hugepage_vma_check(vma, vma->vm_flags, false))
> > > > return SCAN_VMA_CHECK;
> > > > return 0;
> > > > }
> > > > @@ -1442,7 +1399,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
> > > > * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
> > > > * will not fail the vma for missing VM_HUGEPAGE
> > > > */
> > > > - if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
> > > > + if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE, false))
> > > > return;
> > > >
> > > > /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
> > > > @@ -2132,7 +2089,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
> > > > progress++;
> > > > break;
> > > > }
> > > > - if (!hugepage_vma_check(vma, vma->vm_flags)) {
> > > > + if (!hugepage_vma_check(vma, vma->vm_flags, false)) {
> > > > skip:
> > > > progress++;
> > > > continue;
> > > > --
> > > > 2.26.3
> > > >
> > > >
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