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Date: Tue, 29 Aug 2017 22:59:11 -0400
From: Jerome Glisse <jglisse@...hat.com>
To: Nadav Amit <nadav.amit@...il.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
Dan Williams <dan.j.williams@...el.com>,
Ross Zwisler <ross.zwisler@...ux.intel.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Bernhard Held <berny156@....de>,
Adam Borowski <kilobyte@...band.pl>,
Andrea Arcangeli <aarcange@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Wanpeng Li <kernellwp@...il.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Takashi Iwai <tiwai@...e.de>, Mike Galbraith <efault@....de>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
axie <axie@....com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 02/13] mm/rmap: update to new mmu_notifier semantic
On Tue, Aug 29, 2017 at 07:46:07PM -0700, Nadav Amit wrote:
> Jérôme Glisse <jglisse@...hat.com> wrote:
>
> > Replacing all mmu_notifier_invalidate_page() by mmu_notifier_invalidat_range()
> > and making sure it is bracketed by call to mmu_notifier_invalidate_range_start/
> > end.
> >
> > Note that because we can not presume the pmd value or pte value we have to
> > assume the worse and unconditionaly report an invalidation as happening.
> >
> > Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: Bernhard Held <berny156@....de>
> > Cc: Adam Borowski <kilobyte@...band.pl>
> > Cc: Andrea Arcangeli <aarcange@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Cc: Wanpeng Li <kernellwp@...il.com>
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Takashi Iwai <tiwai@...e.de>
> > Cc: Nadav Amit <nadav.amit@...il.com>
> > Cc: Mike Galbraith <efault@....de>
> > Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Cc: axie <axie@....com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> > mm/rmap.c | 44 +++++++++++++++++++++++++++++++++++++++++---
> > 1 file changed, 41 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index c8993c63eb25..da97ed525088 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -887,11 +887,21 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
> > .address = address,
> > .flags = PVMW_SYNC,
> > };
> > + unsigned long start = address, end;
> > int *cleaned = arg;
> >
> > + /*
> > + * We have to assume the worse case ie pmd for invalidation. Note that
> > + * the page can not be free from this function.
> > + */
> > + end = min(vma->vm_end, (start & PMD_MASK) + PMD_SIZE);
> > + mmu_notifier_invalidate_range_start(vma->vm_mm, start, end);
> > +
> > while (page_vma_mapped_walk(&pvmw)) {
> > + unsigned long cstart, cend;
> > int ret = 0;
> > - address = pvmw.address;
> > +
> > + cstart = address = pvmw.address;
> > if (pvmw.pte) {
> > pte_t entry;
> > pte_t *pte = pvmw.pte;
> > @@ -904,6 +914,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
> > entry = pte_wrprotect(entry);
> > entry = pte_mkclean(entry);
> > set_pte_at(vma->vm_mm, address, pte, entry);
> > + cend = cstart + PAGE_SIZE;
> > ret = 1;
> > } else {
> > #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
> > @@ -918,6 +929,8 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
> > entry = pmd_wrprotect(entry);
> > entry = pmd_mkclean(entry);
> > set_pmd_at(vma->vm_mm, address, pmd, entry);
> > + cstart &= PMD_MASK;
> > + cend = cstart + PMD_SIZE;
> > ret = 1;
> > #else
> > /* unexpected pmd-mapped page? */
> > @@ -926,11 +939,13 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
> > }
> >
> > if (ret) {
> > - mmu_notifier_invalidate_page(vma->vm_mm, address);
> > + mmu_notifier_invalidate_range(vma->vm_mm, cstart, cend);
> > (*cleaned)++;
> > }
> > }
> >
> > + mmu_notifier_invalidate_range_end(vma->vm_mm, start, end);
> > +
> > return true;
> > }
> >
> > @@ -1324,6 +1339,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> > pte_t pteval;
> > struct page *subpage;
> > bool ret = true;
> > + unsigned long start = address, end;
> > enum ttu_flags flags = (enum ttu_flags)arg;
> >
> > /* munlock has nothing to gain from examining un-locked vmas */
> > @@ -1335,6 +1351,14 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> > flags & TTU_MIGRATION, page);
> > }
> >
> > + /*
> > + * We have to assume the worse case ie pmd for invalidation. Note that
> > + * the page can not be free in this function as call of try_to_unmap()
> > + * must hold a reference on the page.
> > + */
> > + end = min(vma->vm_end, (start & PMD_MASK) + PMD_SIZE);
> > + mmu_notifier_invalidate_range_start(vma->vm_mm, start, end);
> > +
> > while (page_vma_mapped_walk(&pvmw)) {
> > /*
> > * If the page is mlock()d, we cannot swap it out.
> > @@ -1408,6 +1432,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> > set_huge_swap_pte_at(mm, address,
> > pvmw.pte, pteval,
> > vma_mmu_pagesize(vma));
> > + mmu_notifier_invalidate_range(mm, address,
> > + address + vma_mmu_pagesize(vma));
>
> I don’t think that the notifier should be called after the PTE is set, but
> after the PTE is cleared, PTE permissions are demoted (e.g., RW->RO) or
> access/dirty bits are cleared. [There is an exception: if the PFN in the PTE
> is changed without clearing the PTE before, but it does not apply here, and
> there is a different notifier for this case.]
>
> Therefore, IIUC, try_to_umap_one() should only call
> mmu_notifier_invalidate_range() after ptep_get_and_clear() and
> ptep_clear_flush() are called. All the other calls to
> mmu_notifier_invalidate_range() in this function can be removed.
Yes it would simplify the patch, i was trying to optimize for the case
where we restore the pte to its original value after ptep_clear_flush()
or ptep_get_and_clear() as in this case there is no need to invalidate
any secondary page table but that's an overkill optimization that just
add too much complexity.
Jérôme
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