On Mon, Mar 13, 2017 at 11:45:02AM -0400, Zi Yan wrote:
> From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
> If one of callers of page migration starts to handle thp,
> memory management code start to see pmd migration entry, so we need
> to prepare for it before enabling. This patch changes various code
> point which checks the status of given pmds in order to prevent race
> between thp migration and the pmd-related works.
>
> ChangeLog v1 -> v2:
> - introduce pmd_related() (I know the naming is not good, but can't
> think up no better name. Any suggesntion is welcomed.)
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
> ChangeLog v2 -> v3:
> - add is_swap_pmd()
> - a pmd entry should be pmd pointing to pte pages, is_swap_pmd(),
> pmd_trans_huge(), pmd_devmap(), or pmd_none()
> - use pmdp_huge_clear_flush() instead of pmdp_huge_get_and_clear()
> - flush_cache_range() while set_pmd_migration_entry()
> - pmd_none_or_trans_huge_or_clear_bad() and pmd_trans_unstable() return
> true on pmd_migration_entry, so that migration entries are not
> treated as pmd page table entries.
>
> Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> ---
> arch/x86/mm/gup.c | 4 +--
> fs/proc/task_mmu.c | 22 +++++++++------
> include/asm-generic/pgtable.h | 3 +-
> include/linux/huge_mm.h | 14 +++++++--
> mm/gup.c | 22 +++++++++++++--
> mm/huge_memory.c | 66 ++++++++++++++++++++++++++++++++++++++-----
> mm/madvise.c | 2 ++
> mm/memcontrol.c | 2 ++
> mm/memory.c | 9 ++++--
> mm/mprotect.c | 6 ++--
> mm/mremap.c | 2 +-
> 11 files changed, 124 insertions(+), 28 deletions(-)
>
> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
> index 1f3b6ef105cd..23bb071f286d 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -243,9 +243,9 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
> pmd_t pmd = *pmdp;
>
> next = pmd_addr_end(addr, end);
> - if (pmd_none(pmd))
> + if (!pmd_present(pmd))
> return 0;
> - if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
> + if (unlikely(pmd_large(pmd))) {
> /*
> * NUMA hinting faults need to be handled in the GUP
> * slowpath for accounting purposes and so that they
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 5c8359704601..f2b0f3ba25ac 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -600,7 +600,8 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>
> ptl = pmd_trans_huge_lock(pmd, vma);
> if (ptl) {
> - smaps_pmd_entry(pmd, addr, walk);
> + if (pmd_present(*pmd))
> + smaps_pmd_entry(pmd, addr, walk);
> spin_unlock(ptl);
> return 0;
> }
> @@ -942,6 +943,9 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> goto out;
> }
>
> + if (!pmd_present(*pmd))
> + goto out;
> +
> page = pmd_page(*pmd);
>
> /* Clear accessed and referenced bits. */
> @@ -1221,19 +1225,19 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
> if (ptl) {
> u64 flags = 0, frame = 0;
> pmd_t pmd = *pmdp;
> + struct page *page;
>
> if ((vma->vm_flags & VM_SOFTDIRTY) || pmd_soft_dirty(pmd))
> flags |= PM_SOFT_DIRTY;
>
> - /*
> - * Currently pmd for thp is always present because thp
> - * can not be swapped-out, migrated, or HWPOISONed
> - * (split in such cases instead.)
> - * This if-check is just to prepare for future implementation.
> - */
> - if (pmd_present(pmd)) {
> - struct page *page = pmd_page(pmd);
> + if (is_pmd_migration_entry(pmd)) {
> + swp_entry_t entry = pmd_to_swp_entry(pmd);
>
> + frame = swp_type(entry) |
> + (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
> + page = migration_entry_to_page(entry);
> + } else if (pmd_present(pmd)) {
> + page = pmd_page(pmd);
> if (page_mapcount(page) == 1)
> flags |= PM_MMAP_EXCLUSIVE;
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index f4ca23b158b3..f98a028100b6 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -790,7 +790,8 @@ static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> barrier();
> #endif
> - if (pmd_none(pmdval) || pmd_trans_huge(pmdval))
> + if (pmd_none(pmdval) || pmd_trans_huge(pmdval)
> + || !pmd_present(pmdval))
> return 1;
pmd_none() check is redundant now.
> if (unlikely(pmd_bad(pmdval))) {
> pmd_clear_bad(pmd);
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 1b81cb57ff0f..6f44a2352597 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -126,7 +126,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> #define split_huge_pmd(__vma, __pmd, __address) \
> do { \
> pmd_t *____pmd = (__pmd); \
> - if (pmd_trans_huge(*____pmd) \
> + if (is_swap_pmd(*____pmd) || pmd_trans_huge(*____pmd) \
> || pmd_devmap(*____pmd)) \
> __split_huge_pmd(__vma, __pmd, __address, \
> false, NULL); \
> @@ -157,12 +157,18 @@ extern spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd,
> struct vm_area_struct *vma);
> extern spinlock_t *__pud_trans_huge_lock(pud_t *pud,
> struct vm_area_struct *vma);
> +
> +static inline int is_swap_pmd(pmd_t pmd)
> +{
> + return !pmd_none(pmd) && !pmd_present(pmd);
> +}
> +
> /* mmap_sem must be held on entry */
> static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
> struct vm_area_struct *vma)
> {
> VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_mm->mmap_sem), vma);
> - if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
> + if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
> return __pmd_trans_huge_lock(pmd, vma);
> else
> return NULL;
> @@ -269,6 +275,10 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
> long adjust_next)
> {
> }
> +static inline int is_swap_pmd(pmd_t pmd)
> +{
> + return 0;
> +}
> static inline spinlock_t *pmd_trans_huge_lock(pmd_t *pmd,
> struct vm_area_struct *vma)
> {
> diff --git a/mm/gup.c b/mm/gup.c
> index 94fab8fa432b..2b1effb16242 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -272,6 +272,15 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> return page;
> return no_page_table(vma, flags);
> }
> + if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
> + return no_page_table(vma, flags);
> + if (!pmd_present(*pmd)) {
> +retry:
> + if (likely(!(flags & FOLL_MIGRATION)))
> + return no_page_table(vma, flags);
> + pmd_migration_entry_wait(mm, pmd);
> + goto retry;
This looks a lot like endless loop if flags contain FOLL_MIGRATION. Hm?
I guess retry label should be on previous line.
> + }
> if (pmd_devmap(*pmd)) {
> ptl = pmd_lock(mm, pmd);
> page = follow_devmap_pmd(vma, address, pmd, flags);
> @@ -286,6 +295,15 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> return no_page_table(vma, flags);
>
> ptl = pmd_lock(mm, pmd);
> + if (unlikely(!pmd_present(*pmd))) {
> +retry_locked:
> + if (likely(!(flags & FOLL_MIGRATION))) {
> + spin_unlock(ptl);
> + return no_page_table(vma, flags);
> + }
> + pmd_migration_entry_wait(mm, pmd);
> + goto retry_locked;
Again. That's doesn't look right..
> + }
> if (unlikely(!pmd_trans_huge(*pmd))) {
> spin_unlock(ptl);
> return follow_page_pte(vma, address, pmd, flags);
> @@ -341,7 +359,7 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
> pud = pud_offset(pgd, address);
> BUG_ON(pud_none(*pud));
> pmd = pmd_offset(pud, address);
> - if (pmd_none(*pmd))
> + if (!pmd_present(*pmd))
> return -EFAULT;
> VM_BUG_ON(pmd_trans_huge(*pmd));
> pte = pte_offset_map(pmd, address);
> @@ -1369,7 +1387,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
> pmd_t pmd = READ_ONCE(*pmdp);
>
> next = pmd_addr_end(addr, end);
> - if (pmd_none(pmd))
> + if (!pmd_present(pmd))
> return 0;
>
> if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a9c2a0ef5b9b..3f18452f3eb1 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -898,6 +898,21 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>
> ret = -EAGAIN;
> pmd = *src_pmd;
> +
> + if (unlikely(is_pmd_migration_entry(pmd))) {
Shouldn't you first check that the pmd is not present?
> + swp_entry_t entry = pmd_to_swp_entry(pmd);
> +
> + if (is_write_migration_entry(entry)) {
> + make_migration_entry_read(&entry);
> + pmd = swp_entry_to_pmd(entry);
> + set_pmd_at(src_mm, addr, src_pmd, pmd);
> + }
> + set_pmd_at(dst_mm, addr, dst_pmd, pmd);
> + ret = 0;
> + goto out_unlock;
> + }
> + WARN_ONCE(!pmd_present(pmd), "Uknown non-present format on pmd.\n");
Typo.
> +
> if (unlikely(!pmd_trans_huge(pmd))) {
> pte_free(dst_mm, pgtable);
> goto out_unlock;
> @@ -1204,6 +1219,9 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
> if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
> goto out_unlock;j
>
> + if (unlikely(!pmd_present(orig_pmd)))
> + goto out_unlock;
> +
> page = pmd_page(orig_pmd);
> VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
> /*
> @@ -1338,7 +1356,15 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
> goto out;
>
> - page = pmd_page(*pmd);
> + if (is_pmd_migration_entry(*pmd)) {
Again, I don't think it's it's safe to check if pmd is migration entry
before checking if it's present.
> + swp_entry_t entry;
> +
> + entry = pmd_to_swp_entry(*pmd);
> + page = pfn_to_page(swp_offset(entry));
> + if (!is_migration_entry(entry))
> + goto out;
I don't understand how it suppose to work.
You take swp_offset() of entry before checking if it's migration entry.
What's going on?
> + } else
> + page = pmd_page(*pmd);
> VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
> if (flags & FOLL_TOUCH)
> touch_pmd(vma, addr, pmd);
> @@ -1534,6 +1560,9 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> if (is_huge_zero_pmd(orig_pmd))
> goto out;
>
> + if (unlikely(!pmd_present(orig_pmd)))
> + goto out;
> +
> page = pmd_page(orig_pmd);
> /*
> * If other processes are mapping this page, we couldn't discard
> @@ -1766,6 +1795,20 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> if (prot_numa && pmd_protnone(*pmd))
> goto unlock;
>
> + if (is_pmd_migration_entry(*pmd)) {
> + swp_entry_t entry = pmd_to_swp_entry(*pmd);
> +
> + if (is_write_migration_entry(entry)) {
> + pmd_t newpmd;
> +
> + make_migration_entry_read(&entry);
> + newpmd = swp_entry_to_pmd(entry);
> + set_pmd_at(mm, addr, pmd, newpmd);
> + }
> + goto unlock;
> + } else if (!pmd_present(*pmd))
> + WARN_ONCE(1, "Uknown non-present format on pmd.\n");
Another typo.
--
Kirill A. Shutemov
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