Re: [PATCH v2 05/12] mm: thp: add core routines for thp/pmd migration

From: Naoya Horiguchi
Date: Mon Nov 14 2016 - 23:59:25 EST

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In reply to: Kirill A. Shutemov: "Re: [PATCH v2 05/12] mm: thp: add core routines for thp/pmd migration"
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On Mon, Nov 14, 2016 at 02:45:03PM +0300, Kirill A. Shutemov wrote:
> On Tue, Nov 08, 2016 at 08:31:50AM +0900, Naoya Horiguchi wrote:
> > This patch prepares thp migration's core code. These code will be open when
> > unmap_and_move() stops unconditionally splitting thp and get_new_page() starts
> > to allocate destination thps.
> >
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> > ---
> > ChangeLog v1 -> v2:
> > - support pte-mapped thp, doubly-mapped thp
> > ---
> > arch/x86/include/asm/pgtable_64.h | 2 +
> > include/linux/swapops.h | 61 +++++++++++++++
> > mm/huge_memory.c | 154 ++++++++++++++++++++++++++++++++++++++
> > mm/migrate.c | 44 ++++++++++-
> > mm/pgtable-generic.c | 3 +-
> > 5 files changed, 262 insertions(+), 2 deletions(-)
> >
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/arch/x86/include/asm/pgtable_64.h v4.9-rc2-mmotm-2016-10-27-18-27_patched/arch/x86/include/asm/pgtable_64.h
> > index 1cc82ec..3a1b48e 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/arch/x86/include/asm/pgtable_64.h
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/arch/x86/include/asm/pgtable_64.h
> > @@ -167,7 +167,9 @@ static inline int pgd_large(pgd_t pgd) { return 0; }
> > ((type) << (SWP_TYPE_FIRST_BIT)) \
> > | ((offset) << SWP_OFFSET_FIRST_BIT) })
> > #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) })
> > +#define __pmd_to_swp_entry(pte) ((swp_entry_t) { pmd_val((pmd)) })
> > #define __swp_entry_to_pte(x) ((pte_t) { .pte = (x).val })
> > +#define __swp_entry_to_pmd(x) ((pmd_t) { .pmd = (x).val })
> >
> > extern int kern_addr_valid(unsigned long addr);
> > extern void cleanup_highmap(void);
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/include/linux/swapops.h v4.9-rc2-mmotm-2016-10-27-18-27_patched/include/linux/swapops.h
> > index 5c3a5f3..b6b22a2 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/include/linux/swapops.h
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/include/linux/swapops.h
> > @@ -163,6 +163,67 @@ static inline int is_write_migration_entry(swp_entry_t entry)
> >
> > #endif
> >
> > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> > +extern void set_pmd_migration_entry(struct page *page,
> > + struct vm_area_struct *vma, unsigned long address);
> > +
> > +extern int remove_migration_pmd(struct page *new, pmd_t *pmd,
> > + struct vm_area_struct *vma, unsigned long addr, void *old);
> > +
> > +extern void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd);
> > +
> > +static inline swp_entry_t pmd_to_swp_entry(pmd_t pmd)
> > +{
> > + swp_entry_t arch_entry;
> > +
> > + arch_entry = __pmd_to_swp_entry(pmd);
> > + return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
> > +}
> > +
> > +static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
> > +{
> > + swp_entry_t arch_entry;
> > +
> > + arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
> > + return __swp_entry_to_pmd(arch_entry);
> > +}
> > +
> > +static inline int is_pmd_migration_entry(pmd_t pmd)
> > +{
> > + return !pmd_present(pmd) && is_migration_entry(pmd_to_swp_entry(pmd));
> > +}
> > +#else
> > +static inline void set_pmd_migration_entry(struct page *page,
> > + struct vm_area_struct *vma, unsigned long address)
> > +{
>
> VM_BUG()? Or BUILD_BUG()?

These should be compiled out, so BUILD_BUG() seems better to me.
3 routines below will be done in the same manner.

> > +}
> > +
> > +static inline int remove_migration_pmd(struct page *new, pmd_t *pmd,
> > + struct vm_area_struct *vma, unsigned long addr, void *old)
> > +{
> > + return 0;
>
> Ditto.
>
> > +}
> > +
> > +static inline void pmd_migration_entry_wait(struct mm_struct *m, pmd_t *p) { }
> > +
> > +static inline swp_entry_t pmd_to_swp_entry(pmd_t pmd)
> > +{
> > + return swp_entry(0, 0);
>
> Ditto.
>
> > +}
> > +
> > +static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
> > +{
> > + pmd_t pmd = {};
>
> Ditto.
>
> > + return pmd;
> > +}
> > +
> > +static inline int is_pmd_migration_entry(pmd_t pmd)
> > +{
> > + return 0;
> > +}
> > +#endif
> > +
> > #ifdef CONFIG_MEMORY_FAILURE
> >
> > extern atomic_long_t num_poisoned_pages __read_mostly;
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/mm/huge_memory.c v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/huge_memory.c
> > index 0509d17..b3022b3 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/mm/huge_memory.c
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/huge_memory.c
> > @@ -2310,3 +2310,157 @@ static int __init split_huge_pages_debugfs(void)
> > }
> > late_initcall(split_huge_pages_debugfs);
> > #endif
> > +
> > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> > +void set_pmd_migration_entry(struct page *page, struct vm_area_struct *vma,
> > + unsigned long addr)
> > +{
> > + struct mm_struct *mm = vma->vm_mm;
> > + pgd_t *pgd;
> > + pud_t *pud;
> > + pmd_t *pmd;
> > + pmd_t pmdval;
> > + swp_entry_t entry;
> > + spinlock_t *ptl;
> > +
> > + pgd = pgd_offset(mm, addr);
> > + if (!pgd_present(*pgd))
> > + return;
> > + pud = pud_offset(pgd, addr);
> > + if (!pud_present(*pud))
> > + return;
> > + pmd = pmd_offset(pud, addr);
> > + pmdval = *pmd;
> > + barrier();
> > + if (!pmd_present(pmdval))
> > + return;
> > +
> > + mmu_notifier_invalidate_range_start(mm, addr, addr + HPAGE_PMD_SIZE);
> > + if (pmd_trans_huge(pmdval)) {
> > + pmd_t pmdswp;
> > +
> > + ptl = pmd_lock(mm, pmd);
> > + if (!pmd_present(*pmd))
> > + goto unlock_pmd;
> > + if (unlikely(!pmd_trans_huge(*pmd)))
> > + goto unlock_pmd;
>
> Just check *pmd == pmdval?

OK.

>
> > + if (pmd_page(*pmd) != page)
> > + goto unlock_pmd;
> > +
> > + pmdval = pmdp_huge_get_and_clear(mm, addr, pmd);
> > + if (pmd_dirty(pmdval))
> > + set_page_dirty(page);
> > + entry = make_migration_entry(page, pmd_write(pmdval));
> > + pmdswp = swp_entry_to_pmd(entry);
> > + pmdswp = pmd_mkhuge(pmdswp);
> > + set_pmd_at(mm, addr, pmd, pmdswp);
> > + page_remove_rmap(page, true);
> > + put_page(page);
> > +unlock_pmd:
> > + spin_unlock(ptl);
> > + } else { /* pte-mapped thp */
> > + pte_t *pte;
> > + pte_t pteval;
> > + struct page *tmp = compound_head(page);
> > + unsigned long address = addr & HPAGE_PMD_MASK;
> > + pte_t swp_pte;
> > + int i;
> > +
> > + pte = pte_offset_map(pmd, address);
> > + ptl = pte_lockptr(mm, pmd);
> > + spin_lock(ptl);
>
> pte_offset_map_lock() ?

Right.

> > + for (i = 0; i < HPAGE_PMD_NR; i++, pte++, tmp++) {
> > + if (!(pte_present(*pte) &&
> > + page_to_pfn(tmp) == pte_pfn(*pte)))
>
> if (!pte_present(*pte) || pte_page(*pte) != tmp) ?

Yes, this is shorter/simpler.

>
> > + continue;
> > + pteval = ptep_clear_flush(vma, address, pte);
> > + if (pte_dirty(pteval))
> > + set_page_dirty(tmp);
> > + entry = make_migration_entry(tmp, pte_write(pteval));
> > + swp_pte = swp_entry_to_pte(entry);
> > + set_pte_at(mm, address, pte, swp_pte);
> > + page_remove_rmap(tmp, false);
> > + put_page(tmp);
> > + }
> > + pte_unmap_unlock(pte, ptl);
> > + }
> > + mmu_notifier_invalidate_range_end(mm, addr, addr + HPAGE_PMD_SIZE);
> > + return;
> > +}
> > +
> > +int remove_migration_pmd(struct page *new, pmd_t *pmd,
> > + struct vm_area_struct *vma, unsigned long addr, void *old)
> > +{
> > + struct mm_struct *mm = vma->vm_mm;
> > + spinlock_t *ptl;
> > + pmd_t pmde;
> > + swp_entry_t entry;
> > +
> > + pmde = *pmd;
> > + barrier();
> > +
> > + if (!pmd_present(pmde)) {
> > + if (is_migration_entry(pmd_to_swp_entry(pmde))) {
>
> if (!is_migration_entry(pmd_to_swp_entry(pmde)))
> return SWAP_AGAIN;
>
> And one level less indentation below.

OK.

> > + unsigned long mmun_start = addr & HPAGE_PMD_MASK;
> > + unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
> > +
> > + ptl = pmd_lock(mm, pmd);
> > + entry = pmd_to_swp_entry(*pmd);
> > + if (migration_entry_to_page(entry) != old)
> > + goto unlock_ptl;
> > + get_page(new);
> > + pmde = pmd_mkold(mk_huge_pmd(new, vma->vm_page_prot));
> > + if (is_write_migration_entry(entry))
> > + pmde = maybe_pmd_mkwrite(pmde, vma);
> > + flush_cache_range(vma, mmun_start, mmun_end);
> > + page_add_anon_rmap(new, vma, mmun_start, true);
> > + pmdp_huge_clear_flush_notify(vma, mmun_start, pmd);
> > + set_pmd_at(mm, mmun_start, pmd, pmde);
> > + flush_tlb_range(vma, mmun_start, mmun_end);
> > + if (vma->vm_flags & VM_LOCKED)
> > + mlock_vma_page(new);
> > + update_mmu_cache_pmd(vma, addr, pmd);
> > +unlock_ptl:
> > + spin_unlock(ptl);
>
> return SWAP_AGAIN;
>
> And one level less indentation below.
>
> > + }
> > + } else { /* pte-mapped thp */
> > + pte_t *ptep;
> > + pte_t pte;
> > + int i;
> > + struct page *tmpnew = compound_head(new);
> > + struct page *tmpold = compound_head((struct page *)old);
> > + unsigned long address = addr & HPAGE_PMD_MASK;
> > +
> > + ptep = pte_offset_map(pmd, addr);
> > + ptl = pte_lockptr(mm, pmd);
> > + spin_lock(ptl);
>
> pte_offset_map_lock() ?
>
> > +
> > + for (i = 0; i < HPAGE_PMD_NR;
> > + i++, ptep++, tmpnew++, tmpold++, address += PAGE_SIZE) {
> > + pte = *ptep;
> > + if (!is_swap_pte(pte))
> > + continue;
> > + entry = pte_to_swp_entry(pte);
> > + if (!is_migration_entry(entry) ||
> > + migration_entry_to_page(entry) != tmpold)
> > + continue;
> > + get_page(tmpnew);
> > + pte = pte_mkold(mk_pte(tmpnew,
> > + READ_ONCE(vma->vm_page_prot)));
>
> READ_ONCE()? Do we get here under mmap_sem, right?

Some callers of page migration (mbind, move_pages, migrate_pages, cpuset)
do get mmap_sem, but others (memory hotremove, soft offline) don't.
For this part, I borrowed some code from remove_migration_pte() which was
updated at the following commit:

commit 6d2329f8872f23e46a19d240930571510ce525eb
Author: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Date: Fri Oct 7 17:01:22 2016 -0700

mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE

Thank you for reviewing in detail!

Naoya Horiguchi

> > + if (pte_swp_soft_dirty(*ptep))
> > + pte = pte_mksoft_dirty(pte);
> > + if (is_write_migration_entry(entry))
> > + pte = maybe_mkwrite(pte, vma);
> > + flush_dcache_page(tmpnew);
> > + set_pte_at(mm, address, ptep, pte);
> > + if (PageAnon(new))
> > + page_add_anon_rmap(tmpnew, vma, address, false);
> > + else
> > + page_add_file_rmap(tmpnew, false);
> > + update_mmu_cache(vma, address, ptep);
> > + }
> > + pte_unmap_unlock(ptep, ptl);
> > + }
> > + return SWAP_AGAIN;
> > +}
> > +#endif
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/mm/migrate.c v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/migrate.c
> > index 66ce6b4..54f2eb6 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/mm/migrate.c
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/migrate.c
> > @@ -198,6 +198,8 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
> > {
> > struct mm_struct *mm = vma->vm_mm;
> > swp_entry_t entry;
> > + pgd_t *pgd;
> > + pud_t *pud;
> > pmd_t *pmd;
> > pte_t *ptep, pte;
> > spinlock_t *ptl;
> > @@ -208,10 +210,29 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
> > goto out;
> > ptl = huge_pte_lockptr(hstate_vma(vma), mm, ptep);
> > } else {
> > - pmd = mm_find_pmd(mm, addr);
> > + pmd_t pmde;
> > +
> > + pgd = pgd_offset(mm, addr);
> > + if (!pgd_present(*pgd))
> > + goto out;
> > + pud = pud_offset(pgd, addr);
> > + if (!pud_present(*pud))
> > + goto out;
> > + pmd = pmd_offset(pud, addr);
> > if (!pmd)
> > goto out;
> >
> > + if (PageTransCompound(new)) {
> > + remove_migration_pmd(new, pmd, vma, addr, old);
> > + goto out;
> > + }
> > +
> > + pmde = *pmd;
> > + barrier();
> > +
> > + if (!pmd_present(pmde) || pmd_trans_huge(pmde))
> > + goto out;
> > +
> > ptep = pte_offset_map(pmd, addr);
> >
> > /*
> > @@ -344,6 +365,27 @@ void migration_entry_wait_huge(struct vm_area_struct *vma,
> > __migration_entry_wait(mm, pte, ptl);
> > }
> >
> > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> > +void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
> > +{
> > + spinlock_t *ptl;
> > + struct page *page;
> > +
> > + ptl = pmd_lock(mm, pmd);
> > + if (!is_pmd_migration_entry(*pmd))
> > + goto unlock;
> > + page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
> > + if (!get_page_unless_zero(page))
> > + goto unlock;
> > + spin_unlock(ptl);
> > + wait_on_page_locked(page);
> > + put_page(page);
> > + return;
> > +unlock:
> > + spin_unlock(ptl);
> > +}
> > +#endif
> > +
> > #ifdef CONFIG_BLOCK
> > /* Returns true if all buffers are successfully locked */
> > static bool buffer_migrate_lock_buffers(struct buffer_head *head,
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/mm/pgtable-generic.c v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/pgtable-generic.c
> > index 71c5f91..6012343 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/mm/pgtable-generic.c
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/pgtable-generic.c
> > @@ -118,7 +118,8 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
> > {
> > pmd_t pmd;
> > VM_BUG_ON(address & ~HPAGE_PMD_MASK);
> > - VM_BUG_ON(!pmd_trans_huge(*pmdp) && !pmd_devmap(*pmdp));
> > + VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp) &&
> > + !pmd_devmap(*pmdp));
> > pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
> > flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
> > return pmd;
> > --
> > 2.7.0
> >
>
> --
> Kirill A. Shutemov
>

Next message: Peter Chen: "Re: [PATCH v18 0/4] Introduce usb charger framework to deal with the usb gadget power negotation"
Previous message: Alexei Starovoitov: "Re: [PATCH 00/34] perf clang: Builtin clang and perfhook support"
In reply to: Kirill A. Shutemov: "Re: [PATCH v2 05/12] mm: thp: add core routines for thp/pmd migration"
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