[PATCH v3 2/2] mm: Make alloc_contig_range handle in-use hugetlb pages

[Oscar Salvador]

alloc_contig_range() will fail if it finds a HugeTLB page within the range,
without a chance to handle them. Since HugeTLB pages can be migrated as any
LRU or Movable page, it does not make sense to bail out without trying.
Enable the interface to recognize in-use HugeTLB pages so we can migrate
them, and have much better chances to succeed the call.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
---
 include/linux/hugetlb.h |  5 +++--
 mm/compaction.c         | 12 +++++++++++-
 mm/hugetlb.c            | 21 +++++++++++++++++----
 mm/vmscan.c             |  5 +++--
 4 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 72352d718829..8c17d0dbc87c 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -505,7 +505,7 @@ struct huge_bootmem_page {
 	struct hstate *hstate;
 };
 
-bool isolate_or_dissolve_huge_page(struct page *page);
+bool isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
 struct page *alloc_huge_page(struct vm_area_struct *vma,
 				unsigned long addr, int avoid_reserve);
 struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
@@ -776,7 +776,8 @@ void set_page_huge_active(struct page *page);
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
-static inline bool isolate_or_dissolve_huge_page(struct page *page)
+static inline bool isolate_or_dissolve_huge_page(struct page *page,
+						 struct list_head *list)
 {
 	return false;
 }
diff --git a/mm/compaction.c b/mm/compaction.c
index d52506ed9db7..6d9169e71d61 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -906,9 +906,18 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		}
 
 		if (PageHuge(page) && cc->alloc_contig) {
-			if (!isolate_or_dissolve_huge_page(page))
+			if (!isolate_or_dissolve_huge_page(page, &cc->migratepages))
 				goto isolate_fail;
 
+			if (PageHuge(page)) {
+				/*
+				 * Hugepage was successfully isolated and placed
+				 * on the cc->migratepages list.
+				 */
+				low_pfn += compound_nr(page) - 1;
+				goto isolate_success_no_list;
+			}
+
 			/*
 			 * Ok, the hugepage was dissolved. Now these pages are
 			 * Buddy and cannot be re-allocated because they are
@@ -1053,6 +1062,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 isolate_success:
 		list_add(&page->lru, &cc->migratepages);
+isolate_success_no_list:
 		cc->nr_migratepages += compound_nr(page);
 		nr_isolated += compound_nr(page);
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 56eba64a1d33..95dd54cd53c0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2336,7 +2336,9 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
 		goto unlock;
 	} else if (page_count(old_page)) {
 		/*
-		 * Someone has grabbed the page, fail for now.
+		 * Someone has grabbed the page, return -EBUSY so we give
+		 * isolate_or_dissolve_huge_page a chance to handle an in-use
+		 * page.
 		 */
 		ret = -EBUSY;
 		update_and_free_page(h, new_page);
@@ -2368,11 +2370,12 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
 	return ret;
 }
 
-bool isolate_or_dissolve_huge_page(struct page *page)
+bool isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
 {
 	struct hstate *h = NULL;
 	struct page *head;
 	bool ret = false;
+	bool try_again = true;
 
 	spin_lock(&hugetlb_lock);
 	if (PageHuge(page)) {
@@ -2394,9 +2397,19 @@ bool isolate_or_dissolve_huge_page(struct page *page)
 	 */
 	if (hstate_is_gigantic(h))
 		return ret;
-
-	if (!page_count(head) && alloc_and_dissolve_huge_page(h, head))
+retry:
+	if (page_count(head) && isolate_huge_page(head, list)) {
 		ret = true;
+	} else if (!page_count(head)) {
+		int err = alloc_and_dissolve_huge_page(h, head);
+
+		if (!err) {
+			ret = true;
+		} else if (err == -EBUSY && try_again) {
+			try_again = false;
+			goto retry;
+		}
+	}
 
 	return ret;
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b1b574ad199d..0803adca4469 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1506,8 +1506,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 	LIST_HEAD(clean_pages);
 
 	list_for_each_entry_safe(page, next, page_list, lru) {
-		if (page_is_file_lru(page) && !PageDirty(page) &&
-		    !__PageMovable(page) && !PageUnevictable(page)) {
+		if (!PageHuge(page) && page_is_file_lru(page) &&
+		    !PageDirty(page) && !__PageMovable(page) &&
+		    !PageUnevictable(page)) {
 			ClearPageActive(page);
 			list_move(&page->lru, &clean_pages);
 		}
-- 
2.16.3