1 files changed, 430 insertions, 5 deletions

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 639047cc6ea7..573e4366d3b9 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -14,6 +14,7 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/page_idle.h>
 #include <linux/swapops.h>
+#include <linux/shmem_fs.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -42,7 +43,8 @@ enum scan_result {
 	SCAN_DEL_PAGE_LRU,
 	SCAN_ALLOC_HUGE_PAGE_FAIL,
 	SCAN_CGROUP_CHARGE_FAIL,
-	SCAN_EXCEED_SWAP_PTE
+	SCAN_EXCEED_SWAP_PTE,
+	SCAN_TRUNCATED,
 };
 
 #define CREATE_TRACE_POINTS
@@ -294,7 +296,7 @@ struct attribute_group khugepaged_attr_group = {
 	.name = "khugepaged",
 };
 
-#define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
+#define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
 
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)
@@ -816,6 +818,10 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
 	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
 	    (vma->vm_flags & VM_NOHUGEPAGE))
 		return false;
+	if (shmem_file(vma->vm_file)) {
+		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
+				HPAGE_PMD_NR);
+	}
 	if (!vma->anon_vma || vma->vm_ops)
 		return false;
 	if (is_vma_temporary_stack(vma))
@@ -1216,6 +1222,412 @@ static void collect_mm_slot(struct mm_slot *mm_slot)
 	}
 }
 
+#ifdef CONFIG_SHMEM
+static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
+{
+	struct vm_area_struct *vma;
+	unsigned long addr;
+	pmd_t *pmd, _pmd;
+
+	i_mmap_lock_write(mapping);
+	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
+		/* probably overkill */
+		if (vma->anon_vma)
+			continue;
+		addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+		if (addr & ~HPAGE_PMD_MASK)
+			continue;
+		if (vma->vm_end < addr + HPAGE_PMD_SIZE)
+			continue;
+		pmd = mm_find_pmd(vma->vm_mm, addr);
+		if (!pmd)
+			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.
+		 */
+		if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
+			spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
+			/* assume page table is clear */
+			_pmd = pmdp_collapse_flush(vma, addr, pmd);
+			spin_unlock(ptl);
+			up_write(&vma->vm_mm->mmap_sem);
+			atomic_long_dec(&vma->vm_mm->nr_ptes);
+			pte_free(vma->vm_mm, pmd_pgtable(_pmd));
+		}
+	}
+	i_mmap_unlock_write(mapping);
+}
+
+/**
+ * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
+ *
+ * Basic scheme is simple, details are more complex:
+ *  - allocate and freeze a new huge page;
+ *  - scan over radix tree replacing old pages the new one
+ *    + swap in pages if necessary;
+ *    + fill in gaps;
+ *    + keep old pages around in case if rollback is required;
+ *  - if replacing succeed:
+ *    + copy data over;
+ *    + free old pages;
+ *    + unfreeze huge page;
+ *  - if replacing failed;
+ *    + put all pages back and unfreeze them;
+ *    + restore gaps in the radix-tree;
+ *    + free huge page;
+ */
+static void collapse_shmem(struct mm_struct *mm,
+		struct address_space *mapping, pgoff_t start,
+		struct page **hpage, int node)
+{
+	gfp_t gfp;
+	struct page *page, *new_page, *tmp;
+	struct mem_cgroup *memcg;
+	pgoff_t index, end = start + HPAGE_PMD_NR;
+	LIST_HEAD(pagelist);
+	struct radix_tree_iter iter;
+	void **slot;
+	int nr_none = 0, result = SCAN_SUCCEED;
+
+	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
+
+	/* Only allocate from the target node */
+	gfp = alloc_hugepage_khugepaged_gfpmask() |
+		__GFP_OTHER_NODE | __GFP_THISNODE;
+
+	new_page = khugepaged_alloc_page(hpage, gfp, node);
+	if (!new_page) {
+		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+		goto out;
+	}
+
+	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
+		result = SCAN_CGROUP_CHARGE_FAIL;
+		goto out;
+	}
+
+	new_page->index = start;
+	new_page->mapping = mapping;
+	__SetPageSwapBacked(new_page);
+	__SetPageLocked(new_page);
+	BUG_ON(!page_ref_freeze(new_page, 1));
+
+
+	/*
+	 * At this point the new_page is 'frozen' (page_count() is zero), locked
+	 * and not up-to-date. It's safe to insert it into radix tree, because
+	 * nobody would be able to map it or use it in other way until we
+	 * unfreeze it.
+	 */
+
+	index = start;
+	spin_lock_irq(&mapping->tree_lock);
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
+		int n = min(iter.index, end) - index;
+
+		/*
+		 * Handle holes in the radix tree: charge it from shmem and
+		 * insert relevant subpage of new_page into the radix-tree.
+		 */
+		if (n && !shmem_charge(mapping->host, n)) {
+			result = SCAN_FAIL;
+			break;
+		}
+		nr_none += n;
+		for (; index < min(iter.index, end); index++) {
+			radix_tree_insert(&mapping->page_tree, index,
+					new_page + (index % HPAGE_PMD_NR));
+		}
+
+		/* We are done. */
+		if (index >= end)
+			break;
+
+		page = radix_tree_deref_slot_protected(slot,
+				&mapping->tree_lock);
+		if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
+			spin_unlock_irq(&mapping->tree_lock);
+			/* swap in or instantiate fallocated page */
+			if (shmem_getpage(mapping->host, index, &page,
+						SGP_NOHUGE)) {
+				result = SCAN_FAIL;
+				goto tree_unlocked;
+			}
+			spin_lock_irq(&mapping->tree_lock);
+		} else if (trylock_page(page)) {
+			get_page(page);
+		} else {
+			result = SCAN_PAGE_LOCK;
+			break;
+		}
+
+		/*
+		 * The page must be locked, so we can drop the tree_lock
+		 * without racing with truncate.
+		 */
+		VM_BUG_ON_PAGE(!PageLocked(page), page);
+		VM_BUG_ON_PAGE(!PageUptodate(page), page);
+		VM_BUG_ON_PAGE(PageTransCompound(page), page);
+
+		if (page_mapping(page) != mapping) {
+			result = SCAN_TRUNCATED;
+			goto out_unlock;
+		}
+		spin_unlock_irq(&mapping->tree_lock);
+
+		if (isolate_lru_page(page)) {
+			result = SCAN_DEL_PAGE_LRU;
+			goto out_isolate_failed;
+		}
+
+		if (page_mapped(page))
+			unmap_mapping_range(mapping, index << PAGE_SHIFT,
+					PAGE_SIZE, 0);
+
+		spin_lock_irq(&mapping->tree_lock);
+
+		VM_BUG_ON_PAGE(page_mapped(page), page);
+
+		/*
+		 * The page is expected to have page_count() == 3:
+		 *  - we hold a pin on it;
+		 *  - one reference from radix tree;
+		 *  - one from isolate_lru_page;
+		 */
+		if (!page_ref_freeze(page, 3)) {
+			result = SCAN_PAGE_COUNT;
+			goto out_lru;
+		}
+
+		/*
+		 * Add the page to the list to be able to undo the collapse if
+		 * something go wrong.
+		 */
+		list_add_tail(&page->lru, &pagelist);
+
+		/* Finally, replace with the new page. */
+		radix_tree_replace_slot(slot,
+				new_page + (index % HPAGE_PMD_NR));
+
+		index++;
+		continue;
+out_lru:
+		spin_unlock_irq(&mapping->tree_lock);
+		putback_lru_page(page);
+out_isolate_failed:
+		unlock_page(page);
+		put_page(page);
+		goto tree_unlocked;
+out_unlock:
+		unlock_page(page);
+		put_page(page);
+		break;
+	}
+
+	/*
+	 * Handle hole in radix tree at the end of the range.
+	 * This code only triggers if there's nothing in radix tree
+	 * beyond 'end'.
+	 */
+	if (result == SCAN_SUCCEED && index < end) {
+		int n = end - index;
+
+		if (!shmem_charge(mapping->host, n)) {
+			result = SCAN_FAIL;
+			goto tree_locked;
+		}
+
+		for (; index < end; index++) {
+			radix_tree_insert(&mapping->page_tree, index,
+					new_page + (index % HPAGE_PMD_NR));
+		}
+		nr_none += n;
+	}
+
+tree_locked:
+	spin_unlock_irq(&mapping->tree_lock);
+tree_unlocked:
+
+	if (result == SCAN_SUCCEED) {
+		unsigned long flags;
+		struct zone *zone = page_zone(new_page);
+
+		/*
+		 * Replacing old pages with new one has succeed, now we need to
+		 * copy the content and free old pages.
+		 */
+		list_for_each_entry_safe(page, tmp, &pagelist, lru) {
+			copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
+					page);
+			list_del(&page->lru);
+			unlock_page(page);
+			page_ref_unfreeze(page, 1);
+			page->mapping = NULL;
+			ClearPageActive(page);
+			ClearPageUnevictable(page);
+			put_page(page);
+		}
+
+		local_irq_save(flags);
+		__inc_zone_page_state(new_page, NR_SHMEM_THPS);
+		if (nr_none) {
+			__mod_zone_page_state(zone, NR_FILE_PAGES, nr_none);
+			__mod_zone_page_state(zone, NR_SHMEM, nr_none);
+		}
+		local_irq_restore(flags);
+
+		/*
+		 * Remove pte page tables, so we can re-faulti
+		 * the page as huge.
+		 */
+		retract_page_tables(mapping, start);
+
+		/* Everything is ready, let's unfreeze the new_page */
+		set_page_dirty(new_page);
+		SetPageUptodate(new_page);
+		page_ref_unfreeze(new_page, HPAGE_PMD_NR);
+		mem_cgroup_commit_charge(new_page, memcg, false, true);
+		lru_cache_add_anon(new_page);
+		unlock_page(new_page);
+
+		*hpage = NULL;
+	} else {
+		/* Something went wrong: rollback changes to the radix-tree */
+		shmem_uncharge(mapping->host, nr_none);
+		spin_lock_irq(&mapping->tree_lock);
+		radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
+				start) {
+			if (iter.index >= end)
+				break;
+			page = list_first_entry_or_null(&pagelist,
+					struct page, lru);
+			if (!page || iter.index < page->index) {
+				if (!nr_none)
+					break;
+				/* Put holes back where they were */
+				radix_tree_replace_slot(slot, NULL);
+				nr_none--;
+				continue;
+			}
+
+			VM_BUG_ON_PAGE(page->index != iter.index, page);
+
+			/* Unfreeze the page. */
+			list_del(&page->lru);
+			page_ref_unfreeze(page, 2);
+			radix_tree_replace_slot(slot, page);
+			spin_unlock_irq(&mapping->tree_lock);
+			putback_lru_page(page);
+			unlock_page(page);
+			spin_lock_irq(&mapping->tree_lock);
+		}
+		VM_BUG_ON(nr_none);
+		spin_unlock_irq(&mapping->tree_lock);
+
+		/* Unfreeze new_page, caller would take care about freeing it */
+		page_ref_unfreeze(new_page, 1);
+		mem_cgroup_cancel_charge(new_page, memcg, true);
+		unlock_page(new_page);
+		new_page->mapping = NULL;
+	}
+out:
+	VM_BUG_ON(!list_empty(&pagelist));
+	/* TODO: tracepoints */
+}
+
+static void khugepaged_scan_shmem(struct mm_struct *mm,
+		struct address_space *mapping,
+		pgoff_t start, struct page **hpage)
+{
+	struct page *page = NULL;
+	struct radix_tree_iter iter;
+	void **slot;
+	int present, swap;
+	int node = NUMA_NO_NODE;
+	int result = SCAN_SUCCEED;
+
+	present = 0;
+	swap = 0;
+	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
+	rcu_read_lock();
+	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
+		if (iter.index >= start + HPAGE_PMD_NR)
+			break;
+
+		page = radix_tree_deref_slot(slot);
+		if (radix_tree_deref_retry(page)) {
+			slot = radix_tree_iter_retry(&iter);
+			continue;
+		}
+
+		if (radix_tree_exception(page)) {
+			if (++swap > khugepaged_max_ptes_swap) {
+				result = SCAN_EXCEED_SWAP_PTE;
+				break;
+			}
+			continue;
+		}
+
+		if (PageTransCompound(page)) {
+			result = SCAN_PAGE_COMPOUND;
+			break;
+		}
+
+		node = page_to_nid(page);
+		if (khugepaged_scan_abort(node)) {
+			result = SCAN_SCAN_ABORT;
+			break;
+		}
+		khugepaged_node_load[node]++;
+
+		if (!PageLRU(page)) {
+			result = SCAN_PAGE_LRU;
+			break;
+		}
+
+		if (page_count(page) != 1 + page_mapcount(page)) {
+			result = SCAN_PAGE_COUNT;
+			break;
+		}
+
+		/*
+		 * We probably should check if the page is referenced here, but
+		 * nobody would transfer pte_young() to PageReferenced() for us.
+		 * And rmap walk here is just too costly...
+		 */
+
+		present++;
+
+		if (need_resched()) {
+			cond_resched_rcu();
+			slot = radix_tree_iter_next(&iter);
+		}
+	}
+	rcu_read_unlock();
+
+	if (result == SCAN_SUCCEED) {
+		if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
+			result = SCAN_EXCEED_NONE_PTE;
+		} else {
+			node = khugepaged_find_target_node();
+			collapse_shmem(mm, mapping, start, hpage, node);
+		}
+	}
+
+	/* TODO: tracepoints */
+}
+#else
+static void khugepaged_scan_shmem(struct mm_struct *mm,
+		struct address_space *mapping,
+		pgoff_t start, struct page **hpage)
+{
+	BUILD_BUG();
+}
+#endif
+
 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
 					    struct page **hpage)
 	__releases(&khugepaged_mm_lock)
@@ -1269,6 +1681,8 @@ skip:
 		if (khugepaged_scan.address < hstart)
 			khugepaged_scan.address = hstart;
 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
+		if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
+			goto skip;
 
 		while (khugepaged_scan.address < hend) {
 			int ret;
@@ -1279,9 +1693,20 @@ skip:
 			VM_BUG_ON(khugepaged_scan.address < hstart ||
 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
 				  hend);
-			ret = khugepaged_scan_pmd(mm, vma,
-						  khugepaged_scan.address,
-						  hpage);
+			if (shmem_file(vma->vm_file)) {
+				struct file *file = get_file(vma->vm_file);
+				pgoff_t pgoff = linear_page_index(vma,
+						khugepaged_scan.address);
+				up_read(&mm->mmap_sem);
+				ret = 1;
+				khugepaged_scan_shmem(mm, file->f_mapping,
+						pgoff, hpage);
+				fput(file);
+			} else {
+				ret = khugepaged_scan_pmd(mm, vma,
+						khugepaged_scan.address,
+						hpage);
+			}
 			/* move to next address */
 			khugepaged_scan.address += HPAGE_PMD_SIZE;
 			progress += HPAGE_PMD_NR;