[PATCH 6/9] migrate: enable move_pages() to migrate hugepage

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

This patch extends move_pages() to handle vma with VM_HUGETLB
and enables to migrate hugepage with migrate_pages(2).

We avoid getting refcount on tail pages of hugepage, because unlike thp,
hugepage is not split and we need not care about races with splitting.

And migration of larger (1GB for x86_64) hugepage are not enabled.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 mm/memory.c  |  6 ++++--
 mm/migrate.c | 29 ++++++++++++++++++++---------
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git v3.8.orig/mm/memory.c v3.8/mm/memory.c
index bb1369f..d7cfd11 100644
--- v3.8.orig/mm/memory.c
+++ v3.8/mm/memory.c
@@ -1495,7 +1495,8 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 	if (pud_none(*pud))
 		goto no_page_table;
 	if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
-		BUG_ON(flags & FOLL_GET);
+		if (flags & FOLL_GET)
+			goto out;
 		page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
 		goto out;
 	}
@@ -1506,8 +1507,9 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 	if (pmd_none(*pmd))
 		goto no_page_table;
 	if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
-		BUG_ON(flags & FOLL_GET);
 		page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
+		if (flags & FOLL_GET && PageHead(page))
+			get_page_foll(page);
 		goto out;
 	}
 	if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
diff --git v3.8.orig/mm/migrate.c v3.8/mm/migrate.c
index 7b2ca1a..36959d6 100644
--- v3.8.orig/mm/migrate.c
+++ v3.8/mm/migrate.c
@@ -1130,7 +1130,11 @@ static struct page *new_page_node(struct page *p, unsigned long private,
 
 	*result = &pm->status;
 
-	return alloc_pages_exact_node(pm->node,
+	if (PageHuge(p))
+		return alloc_huge_page_node(page_hstate(compound_head(p)),
+					pm->node);
+	else
+		return alloc_pages_exact_node(pm->node,
 				GFP_HIGHUSER_MOVABLE | GFP_THISNODE, 0);
 }
 
@@ -1176,6 +1180,13 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
 		if (PageReserved(page) || PageKsm(page))
 			goto put_and_set;
 
+		/*
+		 * follow_page(FOLL_GET) didn't get refcount for tail pages of
+		 * hugepage, so here we skip putting it.
+		 */
+		if (PageHuge(page) && PageTail(page))
+			goto set_status;
+
 		pp->page = page;
 		err = page_to_nid(page);
 
@@ -1190,6 +1201,12 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
 				!migrate_all)
 			goto put_and_set;
 
+		if (PageHuge(page)) {
+			get_page(page);
+			list_move_tail(&page->lru, &pagelist);
+			goto put_and_set;
+		}
+
 		err = isolate_lru_page(page);
 		if (!err) {
 			list_add_tail(&page->lru, &pagelist);
@@ -1207,14 +1224,8 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
 		pp->status = err;
 	}
 
-	err = 0;
-	if (!list_empty(&pagelist)) {
-		err = migrate_pages(&pagelist, new_page_node,
-				(unsigned long)pm, 0, MIGRATE_SYNC,
-				MR_SYSCALL);
-		if (err)
-			putback_lru_pages(&pagelist);
-	}
+	err = migrate_movable_pages(&pagelist, new_page_node,
+				(unsigned long)pm, 0, MIGRATE_SYNC, MR_SYSCALL);
 
 	up_read(&mm->mmap_sem);
 	return err;
-- 
1.7.11.7

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