[Devel] Re: [BUGFIX][RFC][PATCH][only -mm] FIX memory leak in memory cgroup vs. page migration [1/1] fix page migration under memory contoller

[KAMEZAWA Hiroyuki]

While using memory control cgroup, page-migration under it works as following.
==
 1. uncharge all refs at try to unmap.
 2. charge regs again remove_migration_ptes()
==
This is simple but has following problems.
==
 The page is uncharged and chaged back again if *mapped*.
    - This means that cgroup before migraion can be different from one after
      migraion
    - If page is not mapped but charged as page cache, charge is just ignored
      (because not mapped, it will not be uncharged before migration)
      This is memory leak.
==
This is bad.
And migration can migrate *not mapped* pages in future by migration-by-kernel
driven by memory-unplug and defragment-by-migration at el.

This patch tries to keep memory cgroup at page migration by increasing
one refcnt during it. 3 functions are added.
 mem_cgroup_prepare_migration() --- increase refcnt of page->page_cgroup
 mem_cgroup_end_migration()     --- decrease refcnt of page->page_cgroup
 mem_cgroup_page_migration() --- copy page->page_cgroup from old page to
                                 new page.

Obviously, mem_cgroup_isolate_pages() and this page migration, which
copies page_cgroup from old page to new page, has race.

There seem to be  3 ways for avoiding this race.
 A. take mem_group->lock while mem_cgroup_page_migration().
 B. isolate pc from mem_cgroup's LRU when we isolate page from zone's LRU.
 C. ignore non-LRU page at mem_cgroup_isolate_pages(). 

This patch uses method (C.) and modifes mem_cgroup_isolate_pages() igonres
!PageLRU pages.

Tested and worked well in ia64/NUMA box.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

---
 include/linux/memcontrol.h |   22 +++++++++++++++
 mm/memcontrol.c            |   62 ++++++++++++++++++++++++++++++++++++++++++---
 mm/migrate.c               |   13 +++++++--
 3 files changed, 90 insertions(+), 7 deletions(-)

Index: linux-2.6.23-rc8-mm2/include/linux/memcontrol.h
===================================================================
--- linux-2.6.23-rc8-mm2.orig/include/linux/memcontrol.h
+++ linux-2.6.23-rc8-mm2/include/linux/memcontrol.h
@@ -43,8 +43,14 @@ extern unsigned long mem_cgroup_isolate_
 					struct mem_cgroup *mem_cont,
 					int active);
 extern void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask);
+
 extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 					gfp_t gfp_mask);
+/* For handling page migration in proper way */
+extern void mem_cgroup_prepare_migration(struct page *page);
+extern void mem_cgroup_end_migration(struct page *page);
+extern void mem_cgroup_page_migration(struct page *newpage, struct page *page);
+
 
 static inline struct mem_cgroup *mm_cgroup(const struct mm_struct *mm)
 {
@@ -107,6 +113,22 @@ static inline struct mem_cgroup *mm_cgro
 	return NULL;
 }
 
+/* For page migration */
+static inline void mem_cgroup_prepare_migration(struct page *page)
+{
+	return;
+}
+
+static inline void mem_cgroup_end_migration(struct mem_cgroup *cgroup)
+{
+	return;
+}
+
+static inline void
+mem_cgroup_page_migration(struct page *newpage, struct page *page)
+{
+	return;
+}
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
Index: linux-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- linux-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ linux-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -198,7 +198,7 @@ unsigned long mem_cgroup_isolate_pages(u
 	unsigned long scan;
 	LIST_HEAD(pc_list);
 	struct list_head *src;
-	struct page_cgroup *pc;
+	struct page_cgroup *pc, *tmp;
 
 	if (active)
 		src = &mem_cont->active_list;
@@ -206,8 +206,10 @@ unsigned long mem_cgroup_isolate_pages(u
 		src = &mem_cont->inactive_list;
 
 	spin_lock(&mem_cont->lru_lock);
-	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
-		pc = list_entry(src->prev, struct page_cgroup, lru);
+	scan = 0;
+	list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
+		if (scan++ >= nr_to_scan)
+			break;
 		page = pc->page;
 		VM_BUG_ON(!pc);
 
@@ -225,9 +227,14 @@ unsigned long mem_cgroup_isolate_pages(u
 		/*
 		 * Reclaim, per zone
 		 * TODO: make the active/inactive lists per zone
+		 * !PageLRU page can be found under us while migration.
+		 * just ignore it.
 		 */
-		if (page_zone(page) != z)
+		if (page_zone(page) != z || !PageLRU(page)) {
+			/* Skip this */
+			/* Don't decrease scan here for avoiding dead lock */
 			continue;
+		}
 
 		/*
 		 * Check if the meta page went away from under us
@@ -417,8 +424,14 @@ void mem_cgroup_uncharge(struct page_cgr
 		return;
 
 	if (atomic_dec_and_test(&pc->ref_cnt)) {
+retry:
 		page = pc->page;
 		lock_page_cgroup(page);
+		/* migration occur ? */
+		if (page_get_page_cgroup(page) != pc) {
+			unlock_page_cgroup(page);
+			goto retry;
+		}
 		mem = pc->mem_cgroup;
 		css_put(&mem->css);
 		page_assign_page_cgroup(page, NULL);
@@ -432,6 +445,47 @@ void mem_cgroup_uncharge(struct page_cgr
 	}
 }
 
+void mem_cgroup_prepare_migration(struct page *page)
+{
+	struct page_cgroup *pc;
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc)
+		atomic_inc(&pc->ref_cnt);
+	unlock_page_cgroup(page);
+	return;
+}
+
+void mem_cgroup_end_migration(struct page *page)
+{
+	struct page_cgroup *pc = page_get_page_cgroup(page);
+	mem_cgroup_uncharge(pc);
+}
+
+void mem_cgroup_page_migration(struct page *newpage, struct page *page)
+{
+	struct page_cgroup *pc;
+	/*
+	* We already keep one reference to paage->cgroup.
+	* and both pages are guaranteed to be locked under page migration.
+	*/
+	lock_page_cgroup(page);
+	lock_page_cgroup(newpage);
+	pc = page_get_page_cgroup(page);
+	if (!pc)
+		goto unlock_out;
+	page_assign_page_cgroup(page, NULL);
+	pc->page = newpage;
+	page_assign_page_cgroup(newpage, pc);
+
+unlock_out:
+	unlock_page_cgroup(newpage);
+	unlock_page_cgroup(page);
+	return;
+}
+
+
+
 int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
 {
 	*tmp = memparse(buf, &buf);
Index: linux-2.6.23-rc8-mm2/mm/migrate.c
===================================================================
--- linux-2.6.23-rc8-mm2.orig/mm/migrate.c
+++ linux-2.6.23-rc8-mm2/mm/migrate.c
@@ -598,9 +598,10 @@ static int move_to_new_page(struct page 
 	else
 		rc = fallback_migrate_page(mapping, newpage, page);
 
-	if (!rc)
+	if (!rc) {
+		mem_cgroup_page_migration(newpage, page);
 		remove_migration_ptes(page, newpage);
-	else
+	} else
 		newpage->mapping = NULL;
 
 	unlock_page(newpage);
@@ -651,6 +652,8 @@ static int unmap_and_move(new_page_t get
 		rcu_read_lock();
 		rcu_locked = 1;
 	}
+	mem_cgroup_prepare_migration(page);
+
 	/*
 	 * This is a corner case handling.
 	 * When a new swap-cache is read into, it is linked to LRU
@@ -666,8 +669,12 @@ static int unmap_and_move(new_page_t get
 	if (!page_mapped(page))
 		rc = move_to_new_page(newpage, page);
 
-	if (rc)
+	if (rc) {
 		remove_migration_ptes(page, page);
+		mem_cgroup_end_migration(page);
+	} else
+		mem_cgroup_end_migration(newpage);
+
 rcu_unlock:
 	if (rcu_locked)
 		rcu_read_unlock();

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