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SubjectRe: [PATCH v5 06/11] mm: thp: check pmd migration entry in common path
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On 04/21/2017 02:17 AM, Zi Yan wrote:
> From: Zi Yan <zi.yan@cs.rutgers.edu>
>
> 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@ah.jp.nec.com>
>
> 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()
> - 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.
>
> ChangeLog v4 -> v5:
> - add explanation in pmd_none_or_trans_huge_or_clear_bad() to state
> the equivalence of !pmd_present() and is_pmd_migration_entry()
> - fix migration entry wait deadlock code (from v1) in follow_page_mask()
> - remove unnecessary code (from v1) in follow_trans_huge_pmd()
> - use is_swap_pmd() instead of !pmd_present() for pmd migration entry,
> so it will not be confused with pmd_none()
> - change author information
>
> Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
> ---
> arch/x86/mm/gup.c | 7 +++--
> fs/proc/task_mmu.c | 30 +++++++++++++--------
> include/asm-generic/pgtable.h | 17 +++++++++++-
> include/linux/huge_mm.h | 14 ++++++++--
> mm/gup.c | 22 ++++++++++++++--
> mm/huge_memory.c | 61 ++++++++++++++++++++++++++++++++++++++-----
> mm/memcontrol.c | 5 ++++
> mm/memory.c | 12 +++++++--
> mm/mprotect.c | 4 +--
> mm/mremap.c | 2 +-
> 10 files changed, 145 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
> index 456dfdfd2249..096bbcc801e6 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -9,6 +9,7 @@
> #include <linux/vmstat.h>
> #include <linux/highmem.h>
> #include <linux/swap.h>
> +#include <linux/swapops.h>
> #include <linux/memremap.h>
>
> #include <asm/mmu_context.h>
> @@ -243,9 +244,11 @@ 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)) {
> + VM_BUG_ON(is_swap_pmd(pmd) && IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(pmd));
> return 0;
> - if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
> + } else 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..57489dcd71c4 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;
> +

These pmd_present() checks should have been done irrespective of the
presence of new PMD migration entries. Please separate them out in a
different clean up patch.

> page = pmd_page(*pmd);
>
> /* Clear accessed and referenced bits. */
> @@ -1221,28 +1225,32 @@ 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 = NULL;
>
> 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 (page_mapcount(page) == 1)
> - flags |= PM_MMAP_EXCLUSIVE;
> + page = pmd_page(pmd);
>
> flags |= PM_PRESENT;
> if (pm->show_pfn)
> frame = pmd_pfn(pmd) +
> ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> + } else if (is_swap_pmd(pmd)) {
> + swp_entry_t entry = pmd_to_swp_entry(pmd);
> +
> + frame = swp_type(entry) |
> + (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
> + flags |= PM_SWAP;
> + VM_BUG_ON(IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(pmd));
> + page = migration_entry_to_page(entry);
> }
>
> + if (page && page_mapcount(page) == 1)
> + flags |= PM_MMAP_EXCLUSIVE;
> +

Yeah, this makes sense. It discovers the page details in case its
a migration PMD entry which never existed before.

> for (; addr != end; addr += PAGE_SIZE) {
> pagemap_entry_t pme = make_pme(frame, flags);
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 1fad160f35de..23bf18116df4 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -809,7 +809,22 @@ 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))
> + /*
> + * !pmd_present() checks for pmd migration entries
> + *
> + * The complete check uses is_pmd_migration_entry() in linux/swapops.h
> + * But using that requires moving current function and pmd_trans_unstable()
> + * to linux/swapops.h to resovle dependency, which is too much code move.
> + *
> + * !pmd_present() is equivalent to is_pmd_migration_entry() currently,
> + * because !pmd_present() pages can only be under migration not swapped
> + * out.
> + *
> + * pmd_none() is preseved for future condition checks on pmd migration
> + * entries and not confusing with this function name, although it is
> + * redundant with !pmd_present().
> + */
> + if (pmd_none(pmdval) || pmd_trans_huge(pmdval) || !pmd_present(pmdval))
> return 1;
> 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 4039ec2993d3..b24c7d10aced 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -278,6 +278,16 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> return page;
> return no_page_table(vma, flags);
> }
> +retry:
> + if (!pmd_present(*pmd)) {
> + if (likely(!(flags & FOLL_MIGRATION)))
> + return no_page_table(vma, flags);
> + VM_BUG_ON(IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(*pmd));
> + if (is_pmd_migration_entry(*pmd))
> + pmd_migration_entry_wait(mm, pmd);
> + goto retry;
> + }
> if (pmd_devmap(*pmd)) {
> ptl = pmd_lock(mm, pmd);
> page = follow_devmap_pmd(vma, address, pmd, flags);
> @@ -291,7 +301,15 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
> return no_page_table(vma, flags);
>
> +retry_locked:
> ptl = pmd_lock(mm, pmd);
> + if (unlikely(!pmd_present(*pmd))) {
> + spin_unlock(ptl);
> + if (likely(!(flags & FOLL_MIGRATION)))
> + return no_page_table(vma, flags);
> + pmd_migration_entry_wait(mm, pmd);
> + goto retry_locked;
> + }
> if (unlikely(!pmd_trans_huge(*pmd))) {
> spin_unlock(ptl);
> return follow_page_pte(vma, address, pmd, flags);
> @@ -350,7 +368,7 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
> pud = pud_offset(p4d, 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);
> @@ -1378,7 +1396,7 @@ 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 7406d88445bf..3479e9caf2fa 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -912,6 +912,22 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>
> ret = -EAGAIN;
> pmd = *src_pmd;
> +
> + if (unlikely(is_swap_pmd(pmd))) {
> + swp_entry_t entry = pmd_to_swp_entry(pmd);
> +
> + VM_BUG_ON(IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(pmd));
> + if (is_write_migration_entry(entry)) {
> + make_migration_entry_read(&entry);

We create a read migration entry after detecting a write ?

> + 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;
> + }
> +
> if (unlikely(!pmd_trans_huge(pmd))) {
> pte_free(dst_mm, pgtable);
> goto out_unlock;
> @@ -1218,6 +1234,9 @@ 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;
>
> + if (unlikely(!pmd_present(orig_pmd)))
> + goto out_unlock;
> +
> page = pmd_page(orig_pmd);
> VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
> /*
> @@ -1548,6 +1567,12 @@ 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))) {
> + VM_BUG_ON(IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(orig_pmd));
> + goto out;
> + }
> +
> page = pmd_page(orig_pmd);
> /*
> * If other processes are mapping this page, we couldn't discard
> @@ -1758,6 +1783,21 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> preserve_write = prot_numa && pmd_write(*pmd);
> ret = 1;
>
> + if (is_swap_pmd(*pmd)) {
> + swp_entry_t entry = pmd_to_swp_entry(*pmd);
> +
> + VM_BUG_ON(IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(*pmd));
> + if (is_write_migration_entry(entry)) {
> + pmd_t newpmd;
> +
> + make_migration_entry_read(&entry);

Same here or maybe I am missing something.

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