mm: thp: check pmd migration entry in common path

When THP migration is being used, memory management code needs to handle
pmd migration entries properly.  This patch uses !pmd_present() or
is_swap_pmd() (depending on whether pmd_none() needs separate code or
not) to check pmd migration entries at the places where a pmd entry is
present.

Since pmd-related code uses split_huge_page(), split_huge_pmd(),
pmd_trans_huge(), pmd_trans_unstable(), or
pmd_none_or_trans_huge_or_clear_bad(), this patch:

1. adds pmd migration entry split code in split_huge_pmd(),

2. takes care of pmd migration entries whenever pmd_trans_huge() is present,

3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware.

Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable()
is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change
them.

Until this commit, a pmd entry should be:
1. pointing to a pte page,
2. is_swap_pmd(),
3. pmd_trans_huge(),
4. pmd_devmap(), or
5. pmd_none().

Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Nellans <dnellans@nvidia.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index a290966..8eec35a 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -608,7 +608,8 @@ 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;
        }
@@ -1012,6 +1013,9 @@ 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. */
@@ -1293,27 +1297,33 @@ 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);
                }
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+               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_pmd_migration_entry(pmd));
+                       page = migration_entry_to_page(entry);
+               }
+#endif
+
+               if (page && page_mapcount(page) == 1)
+                       flags |= PM_MMAP_EXCLUSIVE;
 
                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 4d7bb98..4f93a6d 100644 (file)
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -846,7 +846,23 @@ 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) ||
+               (IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION) && !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 d8f35a0..14bc21c 100644 (file)
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -147,7 +147,7 @@ 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);           \
@@ -178,12 +178,18 @@ 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;
@@ -299,6 +305,10 @@ 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 33d651d..76fd199 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -234,6 +234,16 @@ static struct page *follow_pmd_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(thp_migration_supported() &&
+                                 !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);
@@ -247,7 +257,15 @@ static struct page *follow_pmd_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);
@@ -424,7 +442,7 @@ 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);
@@ -1534,7 +1552,7 @@ 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 937f007..b82585e 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -928,6 +928,23 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
        ret = -EAGAIN;
        pmd = *src_pmd;
+
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+       if (unlikely(is_swap_pmd(pmd))) {
+               swp_entry_t entry = pmd_to_swp_entry(pmd);
+
+               VM_BUG_ON(!is_pmd_migration_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;
+       }
+#endif
+
        if (unlikely(!pmd_trans_huge(pmd))) {
                pte_free(dst_mm, pgtable);
                goto out_unlock;
@@ -1599,6 +1616,12 @@ 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(thp_migration_supported() &&
+                                 !is_pmd_migration_entry(orig_pmd));
+               goto out;
+       }
+
        page = pmd_page(orig_pmd);
        /*
         * If other processes are mapping this page, we couldn't discard
@@ -1810,6 +1833,25 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
        preserve_write = prot_numa && pmd_write(*pmd);
        ret = 1;
 
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+       if (is_swap_pmd(*pmd)) {
+               swp_entry_t entry = pmd_to_swp_entry(*pmd);
+
+               VM_BUG_ON(!is_pmd_migration_entry(*pmd));
+               if (is_write_migration_entry(entry)) {
+                       pmd_t newpmd;
+                       /*
+                        * A protection check is difficult so
+                        * just be safe and disable write
+                        */
+                       make_migration_entry_read(&entry);
+                       newpmd = swp_entry_to_pmd(entry);
+                       set_pmd_at(mm, addr, pmd, newpmd);
+               }
+               goto unlock;
+       }
+#endif
+
        /*
         * Avoid trapping faults against the zero page. The read-only
         * data is likely to be read-cached on the local CPU and
@@ -1875,7 +1917,8 @@ spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
 {
        spinlock_t *ptl;
        ptl = pmd_lock(vma->vm_mm, pmd);
-       if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
+       if (likely(is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) ||
+                       pmd_devmap(*pmd)))
                return ptl;
        spin_unlock(ptl);
        return NULL;
@@ -1993,14 +2036,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
        struct page *page;
        pgtable_t pgtable;
        pmd_t _pmd;
-       bool young, write, dirty, soft_dirty;
+       bool young, write, dirty, soft_dirty, pmd_migration = false;
        unsigned long addr;
        int i;
 
        VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
        VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
        VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
-       VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
+       VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
+                               && !pmd_devmap(*pmd));
 
        count_vm_event(THP_SPLIT_PMD);
 
@@ -2025,7 +2069,16 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
                return __split_huge_zero_page_pmd(vma, haddr, pmd);
        }
 
-       page = pmd_page(*pmd);
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+       pmd_migration = is_pmd_migration_entry(*pmd);
+       if (pmd_migration) {
+               swp_entry_t entry;
+
+               entry = pmd_to_swp_entry(*pmd);
+               page = pfn_to_page(swp_offset(entry));
+       } else
+#endif
+               page = pmd_page(*pmd);
        VM_BUG_ON_PAGE(!page_count(page), page);
        page_ref_add(page, HPAGE_PMD_NR - 1);
        write = pmd_write(*pmd);
@@ -2044,7 +2097,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
                 * transferred to avoid any possibility of altering
                 * permissions across VMAs.
                 */
-               if (freeze) {
+               if (freeze || pmd_migration) {
                        swp_entry_t swp_entry;
                        swp_entry = make_migration_entry(page + i, write);
                        entry = swp_entry_to_pte(swp_entry);
@@ -2143,7 +2196,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
                page = pmd_page(*pmd);
                if (PageMlocked(page))
                        clear_page_mlock(page);
-       } else if (!pmd_devmap(*pmd))
+       } else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
                goto out;
        __split_huge_pmd_locked(vma, pmd, haddr, freeze);
 out:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6532b21..f1f3f5b 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4664,6 +4664,11 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
        struct page *page = NULL;
        enum mc_target_type ret = MC_TARGET_NONE;
 
+       if (unlikely(is_swap_pmd(pmd))) {
+               VM_BUG_ON(thp_migration_supported() &&
+                                 !is_pmd_migration_entry(pmd));
+               return ret;
+       }
        page = pmd_page(pmd);
        VM_BUG_ON_PAGE(!page || !PageHead(page), page);
        if (!(mc.flags & MOVE_ANON))

diff --git a/mm/memory.c b/mm/memory.c
index 13ee83b..886033b 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1065,7 +1065,8 @@ static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src
        src_pmd = pmd_offset(src_pud, addr);
        do {
                next = pmd_addr_end(addr, end);
-               if (pmd_trans_huge(*src_pmd) || pmd_devmap(*src_pmd)) {
+               if (is_swap_pmd(*src_pmd) || pmd_trans_huge(*src_pmd)
+                       || pmd_devmap(*src_pmd)) {
                        int err;
                        VM_BUG_ON_VMA(next-addr != HPAGE_PMD_SIZE, vma);
                        err = copy_huge_pmd(dst_mm, src_mm,
@@ -1326,7 +1327,7 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
        pmd = pmd_offset(pud, addr);
        do {
                next = pmd_addr_end(addr, end);
-               if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
+               if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                        if (next - addr != HPAGE_PMD_SIZE) {
                                VM_BUG_ON_VMA(vma_is_anonymous(vma) &&
                                    !rwsem_is_locked(&tlb->mm->mmap_sem), vma);
@@ -3911,6 +3912,13 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
                pmd_t orig_pmd = *vmf.pmd;
 
                barrier();
+               if (unlikely(is_swap_pmd(orig_pmd))) {
+                       VM_BUG_ON(thp_migration_supported() &&
+                                         !is_pmd_migration_entry(orig_pmd));
+                       if (is_pmd_migration_entry(orig_pmd))
+                               pmd_migration_entry_wait(mm, vmf.pmd);
+                       return 0;
+               }
                if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
                        if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
                                return do_huge_pmd_numa_page(&vmf, orig_pmd);

diff --git a/mm/mprotect.c b/mm/mprotect.c
index bd0f409..a1bfe95 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -149,7 +149,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                unsigned long this_pages;
 
                next = pmd_addr_end(addr, end);
-               if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
+               if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
                                && pmd_none_or_clear_bad(pmd))
                        continue;
 
@@ -159,7 +159,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
                }
 
-               if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
+               if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                        if (next - addr != HPAGE_PMD_SIZE) {
                                __split_huge_pmd(vma, pmd, addr, false, NULL);
                        } else {

diff --git a/mm/mremap.c b/mm/mremap.c
index 7395564..cfec004 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -223,7 +223,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
                new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
                if (!new_pmd)
                        break;
-               if (pmd_trans_huge(*old_pmd)) {
+               if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd)) {
                        if (extent == HPAGE_PMD_SIZE) {
                                bool moved;
                                /* See comment in move_ptes() */