diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index 082d1d2a5216977262d3a1817b30a9131efe873a..bc45ea1efbf7973362c6cb99b433ecba4f95612a 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -15,6 +15,14 @@ extern int __khugepaged_enter(struct mm_struct *mm);
extern void __khugepaged_exit(struct mm_struct *mm);
extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
unsigned long vm_flags);
+#ifdef CONFIG_SHMEM
+extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr);
+#else
+static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
+ unsigned long addr)
+{
+}
+#endif
#define khugepaged_enabled() \
(transparent_hugepage_flags & \
@@ -73,6 +81,10 @@ static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
{
return 0;
}
+static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
+ unsigned long addr)
+{
+}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif /* _LINUX_KHUGEPAGED_H */
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e89430ec5267f941416b1c3818ff10c57624e612..0a1b4b484ac5b4a0eed5e5148f04849d9e09607b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -77,6 +77,8 @@ static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
static struct kmem_cache *mm_slot_cache __read_mostly;
+#define MAX_PTE_MAPPED_THP 8
+
/**
* struct mm_slot - hash lookup from mm to mm_slot
* @hash: hash collision list
@@ -87,6 +89,10 @@ struct mm_slot {
struct hlist_node hash;
struct list_head mm_node;
struct mm_struct *mm;
+
+ /* pte-mapped THP in this mm */
+ int nr_pte_mapped_thp;
+ unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
};
/**
@@ -1254,6 +1260,159 @@ static void collect_mm_slot(struct mm_slot *mm_slot)
}
#if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
+/*
+ * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
+ * khugepaged should try to collapse the page table.
+ */
+static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
+ unsigned long addr)
+{
+ struct mm_slot *mm_slot;
+
+ VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
+
+ spin_lock(&khugepaged_mm_lock);
+ mm_slot = get_mm_slot(mm);
+ if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
+ mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
+ spin_unlock(&khugepaged_mm_lock);
+ return 0;
+}
+
+/**
+ * Try to collapse a pte-mapped THP for mm at address haddr.
+ *
+ * This function checks whether all the PTEs in the PMD are pointing to the
+ * right THP. If so, retract the page table so the THP can refault in with
+ * as pmd-mapped.
+ */
+void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
+{
+ unsigned long haddr = addr & HPAGE_PMD_MASK;
+ struct vm_area_struct *vma = find_vma(mm, haddr);
+ struct page *hpage = NULL;
+ pte_t *start_pte, *pte;
+ pmd_t *pmd, _pmd;
+ spinlock_t *ptl;
+ int count = 0;
+ int i;
+
+ if (!vma || !vma->vm_file ||
+ vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
+ return;
+
+ /*
+ * This vm_flags may not have VM_HUGEPAGE if the page was not
+ * collapsed by this mm. But we can still collapse if the page is
+ * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
+ * will not fail the vma for missing VM_HUGEPAGE
+ */
+ if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
+ return;
+
+ pmd = mm_find_pmd(mm, haddr);
+ if (!pmd)
+ return;
+
+ start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
+
+ /* step 1: check all mapped PTEs are to the right huge page */
+ for (i = 0, addr = haddr, pte = start_pte;
+ i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
+ struct page *page;
+
+ /* empty pte, skip */
+ if (pte_none(*pte))
+ continue;
+
+ /* page swapped out, abort */
+ if (!pte_present(*pte))
+ goto abort;
+
+ page = vm_normal_page(vma, addr, *pte);
+
+ if (!page || !PageCompound(page))
+ goto abort;
+
+ if (!hpage) {
+ hpage = compound_head(page);
+ /*
+ * The mapping of the THP should not change.
+ *
+ * Note that uprobe, debugger, or MAP_PRIVATE may
+ * change the page table, but the new page will
+ * not pass PageCompound() check.
+ */
+ if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
+ goto abort;
+ }
+
+ /*
+ * Confirm the page maps to the correct subpage.
+ *
+ * Note that uprobe, debugger, or MAP_PRIVATE may change
+ * the page table, but the new page will not pass
+ * PageCompound() check.
+ */
+ if (WARN_ON(hpage + i != page))
+ goto abort;
+ count++;
+ }
+
+ /* step 2: adjust rmap */
+ for (i = 0, addr = haddr, pte = start_pte;
+ i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
+ struct page *page;
+
+ if (pte_none(*pte))
+ continue;
+ page = vm_normal_page(vma, addr, *pte);
+ page_remove_rmap(page, false);
+ }
+
+ pte_unmap_unlock(start_pte, ptl);
+
+ /* step 3: set proper refcount and mm_counters. */
+ if (hpage) {
+ page_ref_sub(hpage, count);
+ add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
+ }
+
+ /* step 4: collapse pmd */
+ ptl = pmd_lock(vma->vm_mm, pmd);
+ _pmd = pmdp_collapse_flush(vma, addr, pmd);
+ spin_unlock(ptl);
+ mm_dec_nr_ptes(mm);
+ pte_free(mm, pmd_pgtable(_pmd));
+ return;
+
+abort:
+ pte_unmap_unlock(start_pte, ptl);
+}
+
+static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
+{
+ struct mm_struct *mm = mm_slot->mm;
+ int i;
+
+ if (likely(mm_slot->nr_pte_mapped_thp == 0))
+ return 0;
+
+ if (!down_write_trylock(&mm->mmap_sem))
+ return -EBUSY;
+
+ if (unlikely(khugepaged_test_exit(mm)))
+ goto out;
+
+ for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
+ collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
+
+out:
+ mm_slot->nr_pte_mapped_thp = 0;
+ up_write(&mm->mmap_sem);
+ return 0;
+}
+
static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
{
struct vm_area_struct *vma;
@@ -1262,7 +1421,22 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
i_mmap_lock_write(mapping);
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
- /* probably overkill */
+ /*
+ * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
+ * got written to. These VMAs are likely not worth investing
+ * down_write(mmap_sem) as PMD-mapping is likely to be split
+ * later.
+ *
+ * Not that vma->anon_vma check is racy: it can be set up after
+ * the check but before we took mmap_sem by the fault path.
+ * But page lock would prevent establishing any new ptes of the
+ * page, so we are safe.
+ *
+ * An alternative would be drop the check, but check that page
+ * table is clear before calling pmdp_collapse_flush() under
+ * ptl. It has higher chance to recover THP for the VMA, but
+ * has higher cost too.
+ */
if (vma->anon_vma)
continue;
addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
@@ -1275,9 +1449,10 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
continue;
/*
* We need exclusive mmap_sem to retract page table.
- * If trylock fails we would end up with pte-mapped THP after
- * re-fault. Not ideal, but it's more important to not disturb
- * the system too much.
+ *
+ * We use trylock due to lock inversion: we need to acquire
+ * mmap_sem while holding page lock. Fault path does it in
+ * reverse order. Trylock is a way to avoid deadlock.
*/
if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
@@ -1287,6 +1462,9 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
up_write(&vma->vm_mm->mmap_sem);
mm_dec_nr_ptes(vma->vm_mm);
pte_free(vma->vm_mm, pmd_pgtable(_pmd));
+ } else {
+ /* Try again later */
+ khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
}
}
i_mmap_unlock_write(mapping);
@@ -1709,6 +1887,11 @@ static void khugepaged_scan_file(struct mm_struct *mm,
{
BUILD_BUG();
}
+
+static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
+{
+ return 0;
+}
#endif
static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
@@ -1733,6 +1916,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
khugepaged_scan.mm_slot = mm_slot;
}
spin_unlock(&khugepaged_mm_lock);
+ khugepaged_collapse_pte_mapped_thps(mm_slot);
mm = mm_slot->mm;
/*