This set is a fix for memory cgroup against 2.6.23-rc8-mm2.
Not including any new feature.

If this is merged to the next -mm, I'm happy.

Patches:
[1/5] ... fix refcnt handling in charge mem_cgroup_charge()
[2/5] ... fix error handling path in mem_cgroup_charge()
[3/5] ... check page->cgroup under lock again.
[4/5] ... fix mem_cgroup_isolate_pages() to skip !PageLRU() pages.
[5/5] ... fix page migration under memory controller, fixes leak.

Changes from previous ones.
 -- dropped new feature.... force_empty patch. It will be posted later.
 -- fix typos
 -- added comments

Tested on x86-64/fake-NUMA system.

Thanks,
-Kame





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The logic of uncharge is 
 - decrement refcnt -> lock page cgroup -> remove page cgroup.
But the logic of charging is
 - lock page cgroup -> increment refcnt -> return.

Then, one charge will be added to a page_cgroup under being removed.
This makes no big trouble (like panic) but one charge is lost.

This patch add a test at charging to verify page_cgroup's refcnt is
greater than 0. If not, unlock and retry.

Changelog v1->v2:
 * added cpu_relax() before retry.

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


 mm/memcontrol.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -271,14 +271,20 @@ int mem_cgroup_charge(struct page *page,
 	 * to see if the cgroup page already has a page_cgroup associated
 	 * with it
 	 */
+retry:
 	lock_page_cgroup(page);
 	pc = page_get_page_cgroup(page);
 	/*
 	 * The page_cgroup exists and the page has already been accounted
 	 */
 	if (pc) {
-		atomic_inc(&pc->ref_cnt);
-		goto done;
+		if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
+			/* this page is under being uncharged ? */
+			unlock_page_cgroup(page);
+			cpu_relax();
+			goto retry;
+		} else
+			goto done;
 	}
 
 	unlock_page_cgroup(page);

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This unlock_page_cgroup() is unnecessary.

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


 mm/memcontrol.c |    2 --
 1 file changed, 2 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -382,9 +382,7 @@ done:
 	return 0;
 free_pc:
 	kfree(pc);
-	return -ENOMEM;
 err:
-	unlock_page_cgroup(page);
 	return -ENOMEM;
 }
 

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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 charged back again if *mapped*.
    - This means that cgroup before migration can be different from one after
      migration
    - 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 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.

During migration
  - old page is under PG_locked.
  - new page is under PG_locked, too.
  - both old page and new page is not on LRU.

This 3 facts guarantees page_cgroup() migration has no race.

Tested and worked well in x86_64/fake-NUMA box.

Changelog v1 -> v2:
  - reflected comments.
  - divided a patch to !PageLRU patch and migration patch.



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

 include/linux/memcontrol.h |   19 +++++++++++++++++++
 mm/memcontrol.c            |   43 +++++++++++++++++++++++++++++++++++++++++++
 mm/migrate.c               |   14 +++++++++++---
 3 files changed, 73 insertions(+), 3 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/migrate.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/migrate.c
+++ devel-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(page, newpage);
 		remove_migration_ptes(page, newpage);
-	else
+	} else
 		newpage->mapping = NULL;
 
 	unlock_page(newpage);
@@ -619,6 +620,7 @@ static int unmap_and_move(new_page_t get
 	int *result = NULL;
 	struct page *newpage = get_new_page(page, private, &result);
 	int rcu_locked = 0;
+	int charge = 0;
 
 	if (!newpage)
 		return -ENOMEM;
@@ -660,14 +662,20 @@ static int unmap_and_move(new_page_t get
 	 */
 	if (!page->mapping)
 		goto rcu_unlock;
+
+	charge = mem_cgroup_prepare_migration(page);
 	/* Establish migration ptes or remove ptes */
 	try_to_unmap(page, 1);
 
 	if (!page_mapped(page))
 		rc = move_to_new_page(newpage, page);
 
-	if (rc)
+	if (rc) {
 		remove_migration_ptes(page, page);
+		if (charge)
+			mem_cgroup_end_migration(page);
+	} else if (charge)
+		mem_cgroup_end_migration(newpage);
 rcu_unlock:
 	if (rcu_locked)
 		rcu_read_unlock();
Index: devel-2.6.23-rc8-mm2/include/linux/memcontrol.h
===================================================================
--- devel-2.6.23-rc8-mm2.orig/include/linux/memcontrol.h
+++ devel-2.6.23-rc8-mm2/include/linux/memcontrol.h
@@ -56,6 +56,10 @@ static inline void mem_cgroup_uncharge_p
 	mem_cgroup_uncharge(page_get_page_cgroup(page));
 }
 
+extern int mem_cgroup_prepare_migration(struct page *page);
+extern void mem_cgroup_end_migration(struct page *page);
+extern void mem_cgroup_page_migration(struct page *page, struct page *newpage);
+
 #else /* CONFIG_CGROUP_MEM_CONT */
 static inline void mm_init_cgroup(struct mm_struct *mm,
 					struct task_struct *p)
@@ -107,6 +111,21 @@ static inline struct mem_cgroup *mm_cgro
 	return NULL;
 }
 
+static inline int mem_cgroup_prepare_migration(struct page *page)
+{
+	return 0;
+}
+
+static inline void mem_cgroup_end_migration(struct page *page)
+{
+}
+
+static inline void
+mem_cgroup_page_migration(struct page *page, struct page *newpage);
+{
+}
+
+
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -488,6 +488,49 @@ void mem_cgroup_uncharge(struct page_cgr
 		}
 	}
 }
+/*
+ * Returns non-zero if a page (under migration) has valid page_cgroup member.
+ * Refcnt of page_cgroup is incremented.
+ */
+
+int mem_cgroup_prepare_migration(struct page *page)
+{
+	struct page_cgroup *pc;
+	int ret = 0;
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc && atomic_inc_not_zero(&pc->ref_cnt))
+		ret = 1;
+	unlock_page_cgroup(page);
+	return ret;
+}
+
+void mem_cgroup_end_migration(struct page *page)
+{
+	struct page_cgroup *pc = page_get_page_cgroup(page);
+	mem_cgroup_uncharge(pc);
+}
+/*
+ * We know both *page* and *newpage* are now not-on-LRU and Pg_locked.
+ * And no race with uncharge() routines because page_cgroup for *page*
+ * has extra one reference by mem_cgroup_prepare_migration.
+ */
+
+void mem_cgroup_page_migration(struct page *page, struct page *newpage)
+{
+	struct page_cgroup *pc;
+retry:
+	pc = page_get_page_cgroup(page);
+	if (!pc)
+		return;
+	if (clear_page_cgroup(page, pc) != pc)
+		goto retry;
+	pc->page = newpage;
+	lock_page_cgroup(newpage);
+	page_assign_page_cgroup(newpage, pc);
+	unlock_page_cgroup(newpage);
+	return;
+}
 
 int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
 {

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This patch makes mem_cgroup_isolate_pages() to be

  - ignore !PageLRU pages.
  - fixes the bug that isolation makes no progress if page_zone(page) != zone
    page once find. (just increment scan in this case.)

kswapd and memory migration removes a page from list when it handles
a page for reclaiming/migration.

Because __isolate_lru_page() doesn't moves page !PageLRU pages, it will
be safe to avoid touching !PageLRU() page and its page_cgroup.

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

 mm/memcontrol.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -240,7 +240,7 @@ 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;
@@ -248,11 +248,18 @@ 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_taken)
+			break;
 		page = pc->page;
 		VM_BUG_ON(!pc);
 
+		if (unlikely(!PageLRU(page))) {
+			scan--;
+			continue;
+		}
+
 		if (PageActive(page) && !active) {
 			__mem_cgroup_move_lists(pc, true);
 			scan--;

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This patch adds following functions.
   - clear_page_cgroup(page, pc)
   - page_cgroup_assign_new_page_group(page, pc)

Mainly for cleanup.

A manner "check page->cgroup again after lock_page_cgroup()" is
implemented in straight way.

Changelog v1 -> v2:
  - added comments.
  - adder printk in mem_cgroup_uncharge() error path, but this is planned to be
    removed by other patch 
Note:
  - a comment in mem_cgroup_uncharge() will be removed by force-empty patch

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



 mm/memcontrol.c |  100 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 73 insertions(+), 27 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -162,6 +162,48 @@ static void __always_inline unlock_page_
 	bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
 }
 
+/*
+ * Tie new page_cgroup to struct page under lock_page_cgroup()
+ * This can fail if the page has been tied to a page_cgroup.
+ * If success, returns 0.
+ */
+static inline int
+page_cgroup_assign_new_page_cgroup(struct page *page, struct page_cgroup *pc)
+{
+	int ret = 0;
+
+	lock_page_cgroup(page);
+	if (!page_get_page_cgroup(page))
+		page_assign_page_cgroup(page, pc);
+	else /* A page is tied to other pc. */
+		ret = 1;
+	unlock_page_cgroup(page);
+	return ret;
+}
+
+/*
+ * Clear page->page_cgroup member under lock_page_cgroup().
+ * If given "pc" value is different from one page->page_cgroup,
+ * page->cgroup is not cleared.
+ * Returns a value of page->page_cgroup at lock taken.
+ * A can can detect failure of clearing by following
+ *  clear_page_cgroup(page, pc) == pc
+ */
+
+static inline struct page_cgroup *
+clear_page_cgroup(struct page *page, struct page_cgroup *pc)
+{
+	struct page_cgroup *ret;
+	/* lock and clear */
+	lock_page_cgroup(page);
+	ret = page_get_page_cgroup(page);
+	if (likely(ret == pc))
+		page_assign_page_cgroup(page, NULL);
+	unlock_page_cgroup(page);
+	return ret;
+}
+
+
 static void __mem_cgroup_move_lists(struct page_cgroup *pc, bool active)
 {
 	if (active)
@@ -260,7 +302,7 @@ int mem_cgroup_charge(struct page *page,
 				gfp_t gfp_mask)
 {
 	struct mem_cgroup *mem;
-	struct page_cgroup *pc, *race_pc;
+	struct page_cgroup *pc;
 	unsigned long flags;
 	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 
@@ -354,24 +396,20 @@ noreclaim:
 		goto free_pc;
 	}
 
-	lock_page_cgroup(page);
-	/*
-	 * Check if somebody else beat us to allocating the page_cgroup
-	 */
-	race_pc = page_get_page_cgroup(page);
-	if (race_pc) {
-		kfree(pc);
-		pc = race_pc;
-		atomic_inc(&pc->ref_cnt);
-		res_counter_uncharge(&mem->res, PAGE_SIZE);
-		css_put(&mem->css);
-		goto done;
-	}
-
 	atomic_set(&pc->ref_cnt, 1);
 	pc->mem_cgroup = mem;
 	pc->page = page;
-	page_assign_page_cgroup(page, pc);
+	if (page_cgroup_assign_new_page_cgroup(page, pc)) {
+		/*
+		 * an another charge is added to this page already.
+		 * we do take lock_page_cgroup(page) again and read
+		 * page->cgroup, increment refcnt.... just retry is OK.
+		 */
+		res_counter_uncharge(&mem->res, PAGE_SIZE);
+		css_put(&mem->css);
+		kfree(pc);
+		goto retry;
+	}
 
 	spin_lock_irqsave(&mem->lru_lock, flags);
 	list_add(&pc->lru, &mem->active_list);
@@ -422,17 +460,25 @@ void mem_cgroup_uncharge(struct page_cgr
 
 	if (atomic_dec_and_test(&pc->ref_cnt)) {
 		page = pc->page;
-		lock_page_cgroup(page);
-		mem = pc->mem_cgroup;
-		css_put(&mem->css);
-		page_assign_page_cgroup(page, NULL);
-		unlock_page_cgroup(page);
-		res_counter_uncharge(&mem->res, PAGE_SIZE);
-
- 		spin_lock_irqsave(&mem->lru_lock, flags);
- 		list_del_init(&pc->lru);
- 		spin_unlock_irqrestore(&mem->lru_lock, flags);
-		kfree(pc);
+		/*
+		 * get page->cgroup and clear it under lock.
+		 */
+		if (clear_page_cgroup(page, pc) == pc) {
+			mem = pc->mem_cgroup;
+			css_put(&mem->css);
+			res_counter_uncharge(&mem->res, PAGE_SIZE);
+			spin_lock_irqsave(&mem->lru_lock, flags);
+			list_del_init(&pc->lru);
+			spin_unlock_irqrestore(&mem->lru_lock, flags);
+			kfree(pc);
+		} else {
+			/*
+			 * Note:This will be removed when force-empty patch is
+			 * applied. just show warning here.
+			 */
+			printk(KERN_ERR "Race in mem_cgroup_uncharge() ?");
+			dump_stack();
+		}
 	}
 }
 

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KAMEZAWA Hiroyuki wrote:
> +
> +static inline void
> +mem_cgroup_page_migration(struct page *page, struct page *newpage);

Typo, the semicolon needs to go :-)

> +{
> +}
> +
> +

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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On Thu, 11 Oct 2007 17:35:40 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > +
> > +static inline void
> > +mem_cgroup_page_migration(struct page *page, struct page *newpage);
> 
> Typo, the semicolon needs to go :-)
>
Oh, thanks!, will send updated version later.

-Kame 
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KAMEZAWA Hiroyuki wrote:
> This set is a fix for memory cgroup against 2.6.23-rc8-mm2.
> Not including any new feature.
> 
> If this is merged to the next -mm, I'm happy.
> 
> Patches:
> [1/5] ... fix refcnt handling in charge mem_cgroup_charge()
> [2/5] ... fix error handling path in mem_cgroup_charge()
> [3/5] ... check page->cgroup under lock again.
> [4/5] ... fix mem_cgroup_isolate_pages() to skip !PageLRU() pages.
> [5/5] ... fix page migration under memory controller, fixes leak.
> 
> Changes from previous ones.
>  -- dropped new feature.... force_empty patch. It will be posted later.
>  -- fix typos
>  -- added comments
> 
> Tested on x86-64/fake-NUMA system.
> 

I tested the patches, ran kernbench, lmbench and some tests with
parallel containers. Except for the one typo in the page migration
patch, the patches worked quite well. KAMEZAWA-San, could you please
send the updated patch with the compilation fix.

I am yet to test the migration fix (I am yet to get access to a NUMA/
box capable of fake NUMA). I have not measured the performance impact
of these patches.

Andrew, could you please consider these patches for -mm inclusion once
KAMEZAWA-San sends out the fixed migration patch.

> Thanks,
> -Kame
> 
> 
> 
> 
> 


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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Hi, here is fixed one.
thanks,
-Kame
==
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 charged back again if *mapped*.
    - This means that cgroup before migration can be different from one after
      migration
    - 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 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.

During migration
  - old page is under PG_locked.
  - new page is under PG_locked, too.
  - both old page and new page is not on LRU.

This 3 facts guarantees page_cgroup() migration has no race.

Tested and worked well in x86_64/fake-NUMA box.
Changelog v2 -> v3
  - fixed typo in !CONFIG_CGROUP_MEM_CONT case.

Changelog v1 -> v2:
  - reflected comments.
  - divided a patch to !PageLRU patch and migration patch.



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

 include/linux/memcontrol.h |   19 +++++++++++++++++++
 mm/memcontrol.c            |   43 +++++++++++++++++++++++++++++++++++++++++++
 mm/migrate.c               |   14 +++++++++++---
 3 files changed, 73 insertions(+), 3 deletions(-)

Index: devel-2.6.23-rc8-mm2/mm/migrate.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/migrate.c
+++ devel-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(page, newpage);
 		remove_migration_ptes(page, newpage);
-	else
+	} else
 		newpage->mapping = NULL;
 
 	unlock_page(newpage);
@@ -619,6 +620,7 @@ static int unmap_and_move(new_page_t get
 	int *result = NULL;
 	struct page *newpage = get_new_page(page, private, &result);
 	int rcu_locked = 0;
+	int charge = 0;
 
 	if (!newpage)
 		return -ENOMEM;
@@ -660,14 +662,20 @@ static int unmap_and_move(new_page_t get
 	 */
 	if (!page->mapping)
 		goto rcu_unlock;
+
+	charge = mem_cgroup_prepare_migration(page);
 	/* Establish migration ptes or remove ptes */
 	try_to_unmap(page, 1);
 
 	if (!page_mapped(page))
 		rc = move_to_new_page(newpage, page);
 
-	if (rc)
+	if (rc) {
 		remove_migration_ptes(page, page);
+		if (charge)
+			mem_cgroup_end_migration(page);
+	} else if (charge)
+		mem_cgroup_end_migration(newpage);
 rcu_unlock:
 	if (rcu_locked)
 		rcu_read_unlock();
Index: devel-2.6.23-rc8-mm2/include/linux/memcontrol.h
===================================================================
--- devel-2.6.23-rc8-mm2.orig/include/linux/memcontrol.h
+++ devel-2.6.23-rc8-mm2/include/linux/memcontrol.h
@@ -56,6 +56,10 @@ static inline void mem_cgroup_uncharge_p
 	mem_cgroup_uncharge(page_get_page_cgroup(page));
 }
 
+extern int mem_cgroup_prepare_migration(struct page *page);
+extern void mem_cgroup_end_migration(struct page *page);
+extern void mem_cgroup_page_migration(struct page *page, struct page *newpage);
+
 #else /* CONFIG_CGROUP_MEM_CONT */
 static inline void mm_init_cgroup(struct mm_struct *mm,
 					struct task_struct *p)
@@ -107,6 +111,21 @@ static inline struct mem_cgroup *mm_cgro
 	return NULL;
 }
 
+static inline int mem_cgroup_prepare_migration(struct page *page)
+{
+	return 0;
+}
+
+static inline void mem_cgroup_end_migration(struct page *page)
+{
+}
+
+static inline void
+mem_cgroup_page_migration(struct page *page, struct page *newpage)
+{
+}
+
+
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
===================================================================
--- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
+++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
@@ -488,6 +488,49 @@ void mem_cgroup_uncharge(struct page_cgr
 		}
 	}
 }
+/*
+ * Returns non-zero if a page (under migration) has valid page_cgroup member.
+ * Refcnt of page_cgroup is incremented.
+ */
+
+int mem_cgroup_prepare_migration(struct page *page)
+{
+	struct page_cgroup *pc;
+	int ret = 0;
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc && atomic_inc_not_zero(&pc->ref_cnt))
+		ret = 1;
+	unlock_page_cgroup(page);
+	return ret;
+}
+
+void mem_cgroup_end_migration(struct page *page)
+{
+	struct page_cgroup *pc = page_get_page_cgroup(page);
+	mem_cgroup_uncharge(pc);
+}
+/*
+ * We know both *page* and *newpage* are now not-on-LRU and Pg_locked.
+ * And no race with uncharge() routines because page_cgroup for *page*
+ * has extra one reference by mem_cgroup_prepare_migration.
+ */
+
+void mem_cgroup_page_migration(struct page *page, struct page *newpage)
+{
+	struct page_cgroup *pc;
+retry:
+	pc = page_get_page_cgroup(page);
+	if (!pc)
+		return;
+	if (clear_page_cgroup(page, pc) != pc)
+		goto retry;
+	pc->page = newpage;
+	lock_page_cgroup(newpage);
+	page_assign_page_cgroup(newpage, pc);
+	unlock_page_cgroup(newpage);
+	return;
+}
 
 int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
 {

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I'm sorry that this patch needs following fix..
Andrew, could you apply this ?
(All version I sent has this bug....Sigh)

Thanks,
-Kame
==
Bugfix for memory cgroup skip !PageLRU page in mem_cgroup_isolate_pages

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

Index: devel-2.6.23-mm1/mm/memcontrol.c
===================================================================
--- devel-2.6.23-mm1.orig/mm/memcontrol.c
+++ devel-2.6.23-mm1/mm/memcontrol.c
@@ -260,7 +260,7 @@ unsigned long mem_cgroup_isolate_pages(u
 	spin_lock(&mem_cont->lru_lock);
 	scan = 0;
 	list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
-		if (scan++ > nr_taken)
+		if (scan++ > nr_to_scan)
 			break;
 		page = pc->page;
 		VM_BUG_ON(!pc);

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KAMEZAWA Hiroyuki wrote:
> I'm sorry that this patch needs following fix..
> Andrew, could you apply this ?
> (All version I sent has this bug....Sigh)
> 
> Thanks,
> -Kame
> ==
> Bugfix for memory cgroup skip !PageLRU page in mem_cgroup_isolate_pages
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> Index: devel-2.6.23-mm1/mm/memcontrol.c
> ===================================================================
> --- devel-2.6.23-mm1.orig/mm/memcontrol.c
> +++ devel-2.6.23-mm1/mm/memcontrol.c
> @@ -260,7 +260,7 @@ unsigned long mem_cgroup_isolate_pages(u
>  	spin_lock(&mem_cont->lru_lock);
>  	scan = 0;
>  	list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
> -		if (scan++ > nr_taken)
> +		if (scan++ > nr_to_scan)
>  			break;
>  		page = pc->page;
>  		VM_BUG_ON(!pc);
> 

Good catch! Sorry, I missed it in the review

Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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