On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> With new refcounting THP can belong to several VMAs. This makes tricky
> to track THP pages, when they partially mlocked. It can lead to leaking
> mlocked pages to non-VM_LOCKED vmas and other problems.
>
> With this patch we will split all pages on mlock and avoid
> fault-in/collapse new THP in VM_LOCKED vmas.
>
> I've tried alternative approach: do not mark THP pages mlocked and keep
> them on normal LRUs. This way vmscan could try to split huge pages on
> memory pressure and free up subpages which doesn't belong to VM_LOCKED
> vmas. But this is user-visible change: we screw up Mlocked accouting
> reported in meminfo, so I had to leave this approach aside.
>
> We can bring something better later, but this should be good enough for
> now.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> ---
> mm/gup.c | 2 ++
> mm/huge_memory.c | 5 ++++-
> mm/memory.c | 3 ++-
> mm/mlock.c | 51 +++++++++++++++++++--------------------------------
> 4 files changed, 27 insertions(+), 34 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index eaeeae15006b..7334eb24f414 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -882,6 +882,8 @@ long populate_vma_page_range(struct vm_area_struct *vma,
> VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
>
> gup_flags = FOLL_TOUCH | FOLL_POPULATE;
> + if (vma->vm_flags & VM_LOCKED)
> + gup_flags |= FOLL_SPLIT;
> /*
> * We want to touch writable mappings with a write fault in order
> * to break COW, except for shared mappings because these don't COW
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index fd8af5b9917f..fa3d4f78b716 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -796,6 +796,8 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
>
> if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
> return VM_FAULT_FALLBACK;
> + if (vma->vm_flags & VM_LOCKED)
> + return VM_FAULT_FALLBACK;
> if (unlikely(anon_vma_prepare(vma)))
> return VM_FAULT_OOM;
> if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
> @@ -2467,7 +2469,8 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
> if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
> (vma->vm_flags & VM_NOHUGEPAGE))
> return false;
> -
> + if (vma->vm_flags & VM_LOCKED)
> + return false;
> if (!vma->anon_vma || vma->vm_ops)
> return false;
> if (is_vma_temporary_stack(vma))
> diff --git a/mm/memory.c b/mm/memory.c
> index 559c6651d6b6..8bbd3f88544b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2156,7 +2156,8 @@ static int wp_page_copy(struct mm_struct *mm, struct vm_area_struct *vma,
>
> pte_unmap_unlock(page_table, ptl);
> mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
> - if (old_page) {
> + /* THP pages are never mlocked */
> + if (old_page && !PageTransCompound(old_page)) {
> /*
> * Don't let another task, with possibly unlocked vma,
> * keep the mlocked page.
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 6fd2cf15e868..76cde3967483 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -443,39 +443,26 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
> page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
> &page_mask);
>
> - if (page && !IS_ERR(page)) {
> - if (PageTransHuge(page)) {
> - lock_page(page);
> - /*
> - * Any THP page found by follow_page_mask() may
> - * have gotten split before reaching
> - * munlock_vma_page(), so we need to recompute
> - * the page_mask here.
> - */
> - page_mask = munlock_vma_page(page);
> - unlock_page(page);
> - put_page(page); /* follow_page_mask() */
> - } else {
> - /*
> - * Non-huge pages are handled in batches via
> - * pagevec. The pin from follow_page_mask()
> - * prevents them from collapsing by THP.
> - */
> - pagevec_add(&pvec, page);
> - zone = page_zone(page);
> - zoneid = page_zone_id(page);
> + if (page && !IS_ERR(page) && !PageTransCompound(page)) {
> + /*
> + * Non-huge pages are handled in batches via
> + * pagevec. The pin from follow_page_mask()
> + * prevents them from collapsing by THP.
> + */
> + pagevec_add(&pvec, page);
> + zone = page_zone(page);
> + zoneid = page_zone_id(page);
>
> - /*
> - * Try to fill the rest of pagevec using fast
> - * pte walk. This will also update start to
> - * the next page to process. Then munlock the
> - * pagevec.
> - */
> - start = __munlock_pagevec_fill(&pvec, vma,
> - zoneid, start, end);
> - __munlock_pagevec(&pvec, zone);
> - goto next;
> - }
> + /*
> + * Try to fill the rest of pagevec using fast
> + * pte walk. This will also update start to
> + * the next page to process. Then munlock the
> + * pagevec.
> + */
> + start = __munlock_pagevec_fill(&pvec, vma,
> + zoneid, start, end);
> + __munlock_pagevec(&pvec, zone);
> + goto next;
> }
> /* It's a bug to munlock in the middle of a THP page */
> VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);
>
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