[PATCH 3/6] mm: add is_migrate_isolate_page_nolock() for cases where locking is undesirable

[Vlastimil Babka]

This patch complements the addition of get_pageblock_migratetype_nolock() for
the case where is_migrate_isolate_page() cannot be called with zone->lock held.
A race with set_pageblock_migratetype() may be detected, in which case a caller
supplied argument is returned.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 include/linux/page-isolation.h | 24 ++++++++++++++++++++++++
 mm/hugetlb.c                   |  2 +-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 3fff8e7..f7bd491 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -2,10 +2,30 @@
 #define __LINUX_PAGEISOLATION_H
 
 #ifdef CONFIG_MEMORY_ISOLATION
+/*
+ * Should be called only with zone->lock held. In cases where locking overhead
+ * is undesirable, consider the _nolock version.
+ */
 static inline bool is_migrate_isolate_page(struct page *page)
 {
 	return get_pageblock_migratetype(page) == MIGRATE_ISOLATE;
 }
+/*
+ * When called without zone->lock held, a race with set_pageblock_migratetype
+ * may result in bogus values. The race may be detected, in which case the
+ * value of race_fallback argument is returned. For details, see
+ * get_pageblock_migratetype_nolock().
+ */
+static inline bool is_migrate_isolate_page_nolock(struct page *page,
+		bool race_fallback)
+{
+	int migratetype = get_pageblock_migratetype_nolock(page, MIGRATE_TYPES);
+
+	if (unlikely(migratetype == MIGRATE_TYPES))
+		return race_fallback;
+
+	return migratetype == MIGRATE_ISOLATE;
+}
 static inline bool is_migrate_isolate(int migratetype)
 {
 	return migratetype == MIGRATE_ISOLATE;
@@ -15,6 +35,10 @@ static inline bool is_migrate_isolate_page(struct page *page)
 {
 	return false;
 }
+static inline bool is_migrate_isolate_page_nolock(struct page *page)
+{
+	return false;
+}
 static inline bool is_migrate_isolate(int migratetype)
 {
 	return false;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2252cac..fac4003 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -525,7 +525,7 @@ static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
 	struct page *page;
 
 	list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
-		if (!is_migrate_isolate_page(page))
+		if (!is_migrate_isolate_page_nolock(page, true))
 			break;
 	/*
 	 * if 'non-isolated free hugepage' not found on the list,
-- 
1.8.4.5

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