[PATCH] mm: distinguish CMA and MOVABLE isolation in has_unmovable_pages

[Michal Hocko]

Joonsoo has noticed that "mm: drop migrate type checks from
has_unmovable_pages" would break CMA allocator because it relies on
has_unmovable_pages returning false even for CMA pageblocks which in
fact don't have to be movable:
alloc_contig_range
  start_isolate_page_range
    set_migratetype_isolate
      has_unmovable_pages

This is a result of the code sharing between CMA and memory hotplug
while each one has a different idea of what has_unmovable_pages should
return. This is unfortunate but fixing it properly would require a lot
of code duplication.

Fix the issue by introducing the requested migrate type argument
and special case MIGRATE_CMA case where CMA page blocks are handled
properly. This will work for memory hotplug because it requires
MIGRATE_MOVABLE.

Reported-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/page-isolation.h |  2 +-
 mm/page_alloc.c                | 12 +++++++++++-
 mm/page_isolation.c            | 10 +++++-----
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index d4cd2014fa6f..fa9db0c7b54e 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -30,7 +30,7 @@ static inline bool is_migrate_isolate(int migratetype)
 #endif
 
 bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
-			 bool skip_hwpoisoned_pages);
+			 int migratetype, bool skip_hwpoisoned_pages);
 void set_pageblock_migratetype(struct page *page, int migratetype);
 int move_freepages_block(struct zone *zone, struct page *page,
 				int migratetype, int *num_movable);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b4d85ae445c..259aeb22462f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7344,6 +7344,7 @@ void *__init alloc_large_system_hash(const char *tablename,
  * race condition. So you can't expect this function should be exact.
  */
 bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
+			 int migratetype,
 			 bool skip_hwpoisoned_pages)
 {
 	unsigned long pfn, iter, found;
@@ -7356,6 +7357,15 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 	if (zone_idx(zone) == ZONE_MOVABLE)
 		return false;
 
+	/*
+	 * CMA allocations (alloc_contig_range) really need to mark isolate
+	 * CMA pageblocks even when they are not movable in fact so consider
+	 * them movable here.
+	 */
+	if (is_migrate_cma(migratetype) &&
+			is_migrate_cma(get_pageblock_migratetype(page)))
+		return false;
+
 	pfn = page_to_pfn(page);
 	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
 		unsigned long check = pfn + iter;
@@ -7441,7 +7451,7 @@ bool is_pageblock_removable_nolock(struct page *page)
 	if (!zone_spans_pfn(zone, pfn))
 		return false;
 
-	return !has_unmovable_pages(zone, page, 0, true);
+	return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, true);
 }
 
 #if (defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) || defined(CONFIG_CMA)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 757410d9f758..8616f5332c77 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -14,7 +14,7 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/page_isolation.h>
 
-static int set_migratetype_isolate(struct page *page,
+static int set_migratetype_isolate(struct page *page, int migratetype,
 				bool skip_hwpoisoned_pages)
 {
 	struct zone *zone;
@@ -51,7 +51,7 @@ static int set_migratetype_isolate(struct page *page,
 	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
 	 * We just check MOVABLE pages.
 	 */
-	if (!has_unmovable_pages(zone, page, arg.pages_found,
+	if (!has_unmovable_pages(zone, page, arg.pages_found, migratetype,
 				 skip_hwpoisoned_pages))
 		ret = 0;
 
@@ -63,14 +63,14 @@ static int set_migratetype_isolate(struct page *page,
 out:
 	if (!ret) {
 		unsigned long nr_pages;
-		int migratetype = get_pageblock_migratetype(page);
+		int mt = get_pageblock_migratetype(page);
 
 		set_pageblock_migratetype(page, MIGRATE_ISOLATE);
 		zone->nr_isolate_pageblock++;
 		nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
 									NULL);
 
-		__mod_zone_freepage_state(zone, -nr_pages, migratetype);
+		__mod_zone_freepage_state(zone, -nr_pages, mt);
 	}
 
 	spin_unlock_irqrestore(&zone->lock, flags);
@@ -182,7 +182,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
 	     pfn += pageblock_nr_pages) {
 		page = __first_valid_page(pfn, pageblock_nr_pages);
 		if (page &&
-		    set_migratetype_isolate(page, skip_hwpoisoned_pages)) {
+		    set_migratetype_isolate(page, migratetype, skip_hwpoisoned_pages)) {
 			undo_pfn = pfn;
 			goto undo;
 		}
-- 
2.14.2

-- 
Michal Hocko
SUSE Labs