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Message-ID: <YrIU2iP0H5LQbV7R@google.com>
Date: Tue, 21 Jun 2022 11:58:34 -0700
From: Zach O'Keefe <zokeefe@...gle.com>
To: Yang Shi <shy828301@...il.com>
Cc: vbabka@...e.cz, kirill.shutemov@...ux.intel.com,
willy@...radead.org, linmiaohe@...wei.com,
akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [v5 PATCH 4/7] mm: thp: kill transparent_hugepage_active()
On 16 Jun 10:48, Yang Shi 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().
>
> This patch also fixed the wrong behavior for VM_NO_KHUGEPAGED vmas.
>
> Also move hugepage_vma_check() to huge_memory.c and huge_mm.h since it
> is not only for khugepaged anymore.
>
> Reviewed-by: Zach O'Keefe <zokeefe@...gle.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>
> ---
> fs/proc/task_mmu.c | 2 +-
> include/linux/huge_mm.h | 16 +++++++-----
> include/linux/khugepaged.h | 2 --
> mm/huge_memory.c | 50 +++++++++++++++++++++++++++++++-------
> mm/khugepaged.c | 48 +++---------------------------------
> 5 files changed, 56 insertions(+), 62 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 37ccb5c9f4f8..39a40ec181e7 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -863,7 +863,7 @@ 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 8a5a8bfce0f5..64487bcd0c7b 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -202,7 +202,9 @@ 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 & \
> @@ -351,11 +353,6 @@ 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_suitable(struct vm_area_struct *vma,
> unsigned long addr)
> {
> @@ -368,6 +365,13 @@ 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 31ca8a7f78f4..ea5fd4c398f7 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,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index b530462c4493..a28c6100b491 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -69,21 +69,53 @@ 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)
> {
> - /* 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_enabled(vma, vm_flags))
> + return false;
> +
During testing my work on top this patch, I found a small bug here.
Namely, transhuge_vma_enabled() will check vma->vm_mm->flags (to see if
MMF_DISABLE_THP is set); however, for vDSO vmas, vma->vm_mm is NULL.
Previously, transparent_hugepage_active() in smaps path would check
transhuge_vma_suitable() before checking these flags, which would fail for vDSO
vma since we'd take the !vma_is_anonymous() branch and find the vma (most
likely) wasn't suitably aligned (by chance ?).
Anyways, I think we need to check vma->vm_mm.
> + if (vm_flags & VM_NO_KHUGEPAGED)
> + return false;
> +
> + /* Don't run khugepaged against DAX vma */
> + if (vma_is_dax(vma))
> + return false;
>
> - if (!transhuge_vma_suitable(vma, addr))
> + /* Check alignment for file vma and size for both file and anon vma */
> + if (!transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE)))
> return false;
> - 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;
> }
>
> static bool get_huge_zero_page(void)
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 5baa394e34c8..3afd87f8c0b1 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -437,46 +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;
> -
> - /* Check alignment for file vma and size for both file and anon vma */
> - if (!transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE)))
> - 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;
> @@ -513,7 +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);
> }
> }
> @@ -958,7 +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;
> /*
> * Anon VMA expected, the address may be unmapped then
> @@ -1448,7 +1408,7 @@ 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() */
> @@ -2143,7 +2103,7 @@ 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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