mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd

A dax-huge-page mapping while it uses some thp helpers is ultimately not
a transparent huge page.  The distinction is especially important in the
get_user_pages() path.  pmd_devmap() is used to distinguish dax-pmds
from pmd_huge() and pmd_trans_huge() which have slightly different
semantics.

Explicitly mark the pmd_trans_huge() helpers that dax needs by adding
pmd_devmap() checks.

[kirill.shutemov@linux.intel.com: fix regression in handling mlocked pages in  __split_huge_pmd()]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 47 insertions, 27 deletions

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 6585a8b10fea..6a0ad82c8d0f 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -164,13 +164,20 @@ static inline int pmd_large(pmd_t pte)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline int pmd_trans_huge(pmd_t pmd)
 {
-        return pmd_val(pmd) & _PAGE_PSE;
+        return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
 }
 
 static inline int has_transparent_hugepage(void)
 {
         return cpu_has_pse;
 }
+
+#ifdef __HAVE_ARCH_PTE_DEVMAP
+static inline int pmd_devmap(pmd_t pmd)
+{
+        return !!(pmd_val(pmd) & _PAGE_DEVMAP);
+}
+#endif
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 static inline pte_t pte_set_flags(pte_t pte, pteval_t set)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 8ca35a131904..d39fa60bd6bf 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -104,7 +104,8 @@ 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 (pmd_trans_huge(*____pmd)                            \
+                                        || pmd_devmap(*____pmd))        \
                         __split_huge_pmd(__vma, __pmd, __address);      \
         }  while (0)
 
@@ -124,7 +125,7 @@ static inline bool pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
                 spinlock_t **ptl)
 {
         VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_mm->mmap_sem), vma);
-        if (pmd_trans_huge(*pmd))
+        if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
                 return __pmd_trans_huge_lock(pmd, vma, ptl);
         else
                 return false;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a9902152449f..cd123272d28d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -329,6 +329,13 @@ struct inode;
 #define page_private(page)              ((page)->private)
 #define set_page_private(page, v)       ((page)->private = (v))
 
+#if !defined(__HAVE_ARCH_PTE_DEVMAP) || !defined(CONFIG_TRANSPARENT_HUGEPAGE)
+static inline int pmd_devmap(pmd_t pmd)
+{
+        return 0;
+}
+#endif
+
 /*
  * FIXME: take this include out, include page-flags.h in
  * files which need it (119 of them)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d93706013a55..82bed2bec3ed 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -995,7 +995,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
         ret = -EAGAIN;
         pmd = *src_pmd;
-        if (unlikely(!pmd_trans_huge(pmd))) {
+        if (unlikely(!pmd_trans_huge(pmd) && !pmd_devmap(pmd))) {
                 pte_free(dst_mm, pgtable);
                 goto out_unlock;
         }
@@ -1018,17 +1018,20 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                 goto out_unlock;
         }
 
-        src_page = pmd_page(pmd);
-        VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
-        get_page(src_page);
-        page_dup_rmap(src_page, true);
-        add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+        if (pmd_trans_huge(pmd)) {
+                /* thp accounting separate from pmd_devmap accounting */
+                src_page = pmd_page(pmd);
+                VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
+                get_page(src_page);
+                page_dup_rmap(src_page, true);
+                add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+                atomic_long_inc(&dst_mm->nr_ptes);
+                pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
+        }
 
         pmdp_set_wrprotect(src_mm, addr, src_pmd);
         pmd = pmd_mkold(pmd_wrprotect(pmd));
-        pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
-        atomic_long_inc(&dst_mm->nr_ptes);
 
         ret = 0;
 out_unlock:
@@ -1716,7 +1719,7 @@ bool __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)))
+        if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
                 return true;
         spin_unlock(*ptl);
         return false;
@@ -2788,7 +2791,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
         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));
+        VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
 
         count_vm_event(THP_SPLIT_PMD);
 
@@ -2901,14 +2904,15 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 
         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
         ptl = pmd_lock(mm, pmd);
-        if (unlikely(!pmd_trans_huge(*pmd)))
+        if (pmd_trans_huge(*pmd)) {
+                page = pmd_page(*pmd);
+                if (PageMlocked(page))
+                        get_page(page);
+                else
+                        page = NULL;
+        } else if (!pmd_devmap(*pmd))
                 goto out;
-        page = pmd_page(*pmd);
         __split_huge_pmd_locked(vma, pmd, haddr, false);
-        if (PageMlocked(page))
-                get_page(page);
-        else
-                page = NULL;
 out:
         spin_unlock(ptl);
         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
@@ -2938,7 +2942,7 @@ static void split_huge_pmd_address(struct vm_area_struct *vma,
                 return;
 
         pmd = pmd_offset(pud, address);
-        if (!pmd_present(*pmd) || !pmd_trans_huge(*pmd))
+        if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)))
                 return;
         /*
          * Caller holds the mmap_sem write mode, so a huge pmd cannot
diff --git a/mm/memory.c b/mm/memory.c
index 552ae3d69435..ff17850a52d9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -950,7 +950,7 @@ 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)) {
+                if (pmd_trans_huge(*src_pmd) || pmd_devmap(*src_pmd)) {
                         int err;
                         VM_BUG_ON(next-addr != HPAGE_PMD_SIZE);
                         err = copy_huge_pmd(dst_mm, src_mm,
@@ -1177,7 +1177,7 @@ 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)) {
+                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                         if (next - addr != HPAGE_PMD_SIZE) {
 #ifdef CONFIG_DEBUG_VM
                                 if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
@@ -3375,7 +3375,7 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                 int ret;
 
                 barrier();
-                if (pmd_trans_huge(orig_pmd)) {
+                if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
                         unsigned int dirty = flags & FAULT_FLAG_WRITE;
 
                         if (pmd_protnone(orig_pmd))
@@ -3404,7 +3404,7 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
             unlikely(__pte_alloc(mm, vma, pmd, address)))
                 return VM_FAULT_OOM;
         /* if an huge pmd materialized from under us just retry later */
-        if (unlikely(pmd_trans_huge(*pmd)))
+        if (unlikely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
                 return 0;
         /*
          * A regular pmd is established and it can't morph into a huge pmd
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6047707085c1..8eb7bb40dc40 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -149,7 +149,8 @@ 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_none_or_clear_bad(pmd))
+                if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
+                                && pmd_none_or_clear_bad(pmd))
                         continue;
 
                 /* invoke the mmu notifier if the pmd is populated */
@@ -158,7 +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)) {
+                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                         if (next - addr != HPAGE_PMD_SIZE)
                                 split_huge_pmd(vma, pmd, addr);
                         else {
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index c311a2ec6fea..9d4767698a1c 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -132,7 +132,7 @@ 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));
+        VM_BUG_ON(!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;