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Subject[PATCH 3/6] mm: add is_migrate_isolate_page_nolock() for cases where locking is undesirable
Date
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@suse.cz>
---
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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