[PATCH 8/9] memory-hotplug: enable memory hotplug to handle hugepage

[Naoya Horiguchi]

Currently we can't offline memory blocks which contain hugepages because
a hugepage is considered as an unmovable page. But now with this patch
series, a hugepage has become movable, so by using hugepage migration we
can offline such memory blocks.

What's different from other users of hugepage migration is that we need
to decompose all the hugepages inside the target memory block into free
buddy pages after hugepage migration, because otherwise free hugepages
remaining in the memory block intervene the memory offlining.
For this reason we introduce new functions dissolve_free_huge_page() and
dissolve_free_huge_pages().

Other than that, what this patch does is straightforwardly to add hugepage
migration code, that is, adding hugepage code to the functions which scan
over pfn and collect hugepages to be migrated, and adding a hugepage
allocation function to alloc_migrate_target().

As for larger hugepages (1GB for x86_64), it's not easy to do hotremove
over them because it's larger than memory block. So we now simply leave
it to fail as it is.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
 include/linux/hugetlb.h |  8 ++++++++
 mm/hugetlb.c            | 43 +++++++++++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c     | 51 ++++++++++++++++++++++++++++++++++++++++---------
 mm/migrate.c            | 12 +++++++++++-
 mm/page_alloc.c         | 12 ++++++++++++
 mm/page_isolation.c     |  5 +++++
 6 files changed, 121 insertions(+), 10 deletions(-)

diff --git v3.8.orig/include/linux/hugetlb.h v3.8/include/linux/hugetlb.h
index 86a4d78..e33f07f 100644
--- v3.8.orig/include/linux/hugetlb.h
+++ v3.8/include/linux/hugetlb.h
@@ -70,6 +70,7 @@ int dequeue_hwpoisoned_huge_page(struct page *page);
 void putback_active_hugepage(struct page *page);
 void putback_active_hugepages(struct list_head *l);
 void migrate_hugepage_add(struct page *page, struct list_head *list);
+int is_hugepage_movable(struct page *page);
 void copy_huge_page(struct page *dst, struct page *src);
 
 extern unsigned long hugepages_treat_as_movable;
@@ -136,6 +137,7 @@ static inline int dequeue_hwpoisoned_huge_page(struct page *page)
 #define putback_active_hugepage(p) 0
 #define putback_active_hugepages(l) 0
 #define migrate_hugepage_add(p, l) 0
+#define is_hugepage_movable(x) 0
 static inline void copy_huge_page(struct page *dst, struct page *src)
 {
 }
@@ -358,6 +360,10 @@ static inline int hstate_index(struct hstate *h)
 	return h - hstates;
 }
 
+extern void dissolve_free_huge_page(struct page *page);
+extern void dissolve_free_huge_pages(unsigned long start_pfn,
+				     unsigned long end_pfn);
+
 #else
 struct hstate {};
 #define alloc_huge_page(v, a, r) NULL
@@ -378,6 +384,8 @@ static inline unsigned int pages_per_huge_page(struct hstate *h)
 }
 #define hstate_index_to_shift(index) 0
 #define hstate_index(h) 0
+#define dissolve_free_huge_page(p) 0
+#define dissolve_free_huge_pages(s, e) 0
 #endif
 
 #endif /* _LINUX_HUGETLB_H */
diff --git v3.8.orig/mm/hugetlb.c v3.8/mm/hugetlb.c
index ccf9995..c28e6c9 100644
--- v3.8.orig/mm/hugetlb.c
+++ v3.8/mm/hugetlb.c
@@ -843,6 +843,30 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
 	return ret;
 }
 
+/* Dissolve a given free hugepage into free pages. */
+void dissolve_free_huge_page(struct page *page)
+{
+	if (PageHuge(page) && !page_count(page)) {
+		struct hstate *h = page_hstate(page);
+		int nid = page_to_nid(page);
+		spin_lock(&hugetlb_lock);
+		list_del(&page->lru);
+		h->free_huge_pages--;
+		h->free_huge_pages_node[nid]--;
+		update_and_free_page(h, page);
+		spin_unlock(&hugetlb_lock);
+	}
+}
+
+/* Dissolve free hugepages in a given pfn range. Used by memory hotplug. */
+void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
+{
+	unsigned long pfn;
+	unsigned int step = 1 << (HUGETLB_PAGE_ORDER);
+	for (pfn = start_pfn; pfn < end_pfn; pfn += step)
+		dissolve_free_huge_page(pfn_to_page(pfn));
+}
+
 static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
 {
 	struct page *page;
@@ -3158,6 +3182,25 @@ static int is_hugepage_on_freelist(struct page *hpage)
 	return 0;
 }
 
+/* Returns true for head pages of in-use hugepages, otherwise returns false. */
+int is_hugepage_movable(struct page *hpage)
+{
+	struct page *page;
+	struct page *tmp;
+	struct hstate *h = page_hstate(hpage);
+	int ret = 0;
+
+	VM_BUG_ON(!PageHuge(hpage));
+	if (PageTail(hpage))
+		return 0;
+	spin_lock(&hugetlb_lock);
+	list_for_each_entry_safe(page, tmp, &h->hugepage_activelist, lru)
+		if (page == hpage)
+			ret = 1;
+	spin_unlock(&hugetlb_lock);
+	return ret;
+}
+
 /*
  * This function is called from memory failure code.
  * Assume the caller holds page lock of the head page.
diff --git v3.8.orig/mm/memory_hotplug.c v3.8/mm/memory_hotplug.c
index d04ed87..6418de2 100644
--- v3.8.orig/mm/memory_hotplug.c
+++ v3.8/mm/memory_hotplug.c
@@ -29,6 +29,7 @@
 #include <linux/suspend.h>
 #include <linux/mm_inline.h>
 #include <linux/firmware-map.h>
+#include <linux/hugetlb.h>
 
 #include <asm/tlbflush.h>
 
@@ -985,10 +986,12 @@ static int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
 }
 
 /*
- * Scanning pfn is much easier than scanning lru list.
- * Scan pfn from start to end and Find LRU page.
+ * Scan pfn range [start,end) to find movable/migratable pages (LRU pages
+ * and hugepages). We scan pfn because it's much easier than scanning over
+ * linked list. This function returns the pfn of the first found movable
+ * page if it's found, otherwise 0.
  */
-static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
+static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
 {
 	unsigned long pfn;
 	struct page *page;
@@ -997,6 +1000,12 @@ static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
 			page = pfn_to_page(pfn);
 			if (PageLRU(page))
 				return pfn;
+			if (PageHuge(page)) {
+				if (is_hugepage_movable(page))
+					return pfn;
+				else
+					pfn += (1 << compound_order(page)) - 1;
+			}
 		}
 	}
 	return 0;
@@ -1019,6 +1028,30 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 		page = pfn_to_page(pfn);
 		if (!get_page_unless_zero(page))
 			continue;
+		if (PageHuge(page)) {
+			/*
+			 * Larger hugepage (1GB for x86_64) is larger than
+			 * memory block, so pfn scan can start at the tail
+			 * page of larger hugepage. In such case,
+			 * we simply skip the hugepage and move the cursor
+			 * to the last tail page.
+			 */
+			if (PageTail(page)) {
+				struct page *head = compound_head(page);
+				pfn = page_to_pfn(head) +
+					(1 << compound_order(head)) - 1;
+				put_page(page);
+				continue;
+			}
+			pfn = (1 << compound_order(page)) - 1;
+			if (huge_page_size(page_hstate(page)) != PMD_SIZE) {
+				put_page(page);
+				continue;
+			}
+			list_move_tail(&page->lru, &source);
+			move_pages -= 1 << compound_order(page);
+			continue;
+		}
 		/*
 		 * We can skip free pages. And we can only deal with pages on
 		 * LRU.
@@ -1049,7 +1082,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 	}
 	if (!list_empty(&source)) {
 		if (not_managed) {
-			putback_lru_pages(&source);
+			putback_movable_pages(&source);
 			goto out;
 		}
 
@@ -1057,11 +1090,9 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 		 * alloc_migrate_target should be improooooved!!
 		 * migrate_pages returns # of failed pages.
 		 */
-		ret = migrate_pages(&source, alloc_migrate_target, 0,
+		ret = migrate_movable_pages(&source, alloc_migrate_target, 0,
 							true, MIGRATE_SYNC,
 							MR_MEMORY_HOTPLUG);
-		if (ret)
-			putback_lru_pages(&source);
 	}
 out:
 	return ret;
@@ -1304,8 +1335,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
 		drain_all_pages();
 	}
 
-	pfn = scan_lru_pages(start_pfn, end_pfn);
-	if (pfn) { /* We have page on LRU */
+	pfn = scan_movable_pages(start_pfn, end_pfn);
+	if (pfn) { /* We have movable pages */
 		ret = do_migrate_range(pfn, end_pfn);
 		if (!ret) {
 			drain = 1;
@@ -1324,6 +1355,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	yield();
 	/* drain pcp pages, this is synchronous. */
 	drain_all_pages();
+	/* dissolve all free hugepages inside the memory block */
+	dissolve_free_huge_pages(start_pfn, end_pfn);
 	/* check again */
 	offlined_pages = check_pages_isolated(start_pfn, end_pfn);
 	if (offlined_pages < 0) {
diff --git v3.8.orig/mm/migrate.c v3.8/mm/migrate.c
index 8c457e7..a491a98 100644
--- v3.8.orig/mm/migrate.c
+++ v3.8/mm/migrate.c
@@ -1009,8 +1009,18 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 
 	unlock_page(hpage);
 out:
-	if (rc != -EAGAIN)
+	if (rc != -EAGAIN) {
 		putback_active_hugepage(hpage);
+
+		/*
+		 * After hugepage migration from memory hotplug, the original
+		 * hugepage should never be allocated again. This will be
+		 * done by dissolving it into free normal pages, because
+		 * we already set migratetype to MIGRATE_ISOLATE for them.
+		 */
+		if (offlining)
+			dissolve_free_huge_page(hpage);
+	}
 	put_page(new_hpage);
 	if (result) {
 		if (rc)
diff --git v3.8.orig/mm/page_alloc.c v3.8/mm/page_alloc.c
index 6a83cd3..c37951d 100644
--- v3.8.orig/mm/page_alloc.c
+++ v3.8/mm/page_alloc.c
@@ -58,6 +58,7 @@
 #include <linux/prefetch.h>
 #include <linux/migrate.h>
 #include <linux/page-debug-flags.h>
+#include <linux/hugetlb.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -5686,6 +5687,17 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 			continue;
 
 		page = pfn_to_page(check);
+
+		/*
+		 * Hugepages are not in LRU lists, but they're movable.
+		 * We need not scan over tail pages bacause we don't
+		 * handle each tail page individually in migration.
+		 */
+		if (PageHuge(page)) {
+			iter += (1 << compound_order(page)) - 1;
+			continue;
+		}
+
 		/*
 		 * We can't use page_count without pin a page
 		 * because another CPU can free compound page.
diff --git v3.8.orig/mm/page_isolation.c v3.8/mm/page_isolation.c
index 383bdbb..cf48ef6 100644
--- v3.8.orig/mm/page_isolation.c
+++ v3.8/mm/page_isolation.c
@@ -6,6 +6,7 @@
 #include <linux/page-isolation.h>
 #include <linux/pageblock-flags.h>
 #include <linux/memory.h>
+#include <linux/hugetlb.h>
 #include "internal.h"
 
 int set_migratetype_isolate(struct page *page, bool skip_hwpoisoned_pages)
@@ -252,6 +253,10 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private,
 {
 	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
 
+	if (PageHuge(page))
+		return alloc_huge_page_node(page_hstate(compound_head(page)),
+					    numa_node_id());
+
 	if (PageHighMem(page))
 		gfp_mask |= __GFP_HIGHMEM;
 
-- 
1.7.11.7

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