[PATCH V2 2/3] memcg: alter mem_cgroup_{update,inc,dec}_page_stat() args to memcg pointer

[Sha Zhengju <handai.szj@gmail.com>]

From: Sha Zhengju <handai.szj@taobao.com>

Change the first argument of mem_cgroup_{update,inc,dec}_page_stat() from
'struct page *' to 'struct mem_cgroup *', and so move PageCgroupUsed(pc)
checking out of mem_cgroup_update_page_stat(). This is a prepare patch for
the following memcg page stat lock simplifying.

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
---
 include/linux/memcontrol.h |   14 +++++++-------
 mm/memcontrol.c            |    9 ++-------
 mm/rmap.c                  |   28 +++++++++++++++++++++++++---
 3 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d6183f0..7af3ed3 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -163,20 +163,20 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
 	rcu_read_unlock();
 }
 
-void mem_cgroup_update_page_stat(struct page *page,
+void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
 				 enum mem_cgroup_page_stat_item idx,
 				 int val);
 
-static inline void mem_cgroup_inc_page_stat(struct page *page,
+static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
 					    enum mem_cgroup_page_stat_item idx)
 {
-	mem_cgroup_update_page_stat(page, idx, 1);
+	mem_cgroup_update_page_stat(memcg, idx, 1);
 }
 
-static inline void mem_cgroup_dec_page_stat(struct page *page,
+static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
 					    enum mem_cgroup_page_stat_item idx)
 {
-	mem_cgroup_update_page_stat(page, idx, -1);
+	mem_cgroup_update_page_stat(memcg, idx, -1);
 }
 
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
@@ -347,12 +347,12 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
 {
 }
 
-static inline void mem_cgroup_inc_page_stat(struct page *page,
+static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
 					    enum mem_cgroup_page_stat_item idx)
 {
 }
 
-static inline void mem_cgroup_dec_page_stat(struct page *page,
+static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
 					    enum mem_cgroup_page_stat_item idx)
 {
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b31513e..a394ba4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2367,18 +2367,13 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
 	move_unlock_mem_cgroup(pc->mem_cgroup, flags);
 }
 
-void mem_cgroup_update_page_stat(struct page *page,
+void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
 				 enum mem_cgroup_page_stat_item idx, int val)
 {
-	struct mem_cgroup *memcg;
-	struct page_cgroup *pc = lookup_page_cgroup(page);
-	unsigned long uninitialized_var(flags);
-
 	if (mem_cgroup_disabled())
 		return;
 
-	memcg = pc->mem_cgroup;
-	if (unlikely(!memcg || !PageCgroupUsed(pc)))
+	if (unlikely(!memcg))
 		return;
 
 	switch (idx) {
diff --git a/mm/rmap.c b/mm/rmap.c
index 6280da8..a03c2a9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1109,12 +1109,24 @@ void page_add_file_rmap(struct page *page)
 {
 	bool locked;
 	unsigned long flags;
+	struct page_cgroup *pc;
+	struct mem_cgroup *memcg = NULL;
 
 	mem_cgroup_begin_update_page_stat(page, &locked, &flags);
+	pc = lookup_page_cgroup(page);
+
+	rcu_read_lock();
+	memcg = pc->mem_cgroup;
+	if (unlikely(!PageCgroupUsed(pc)))
+		memcg = NULL;
+
 	if (atomic_inc_and_test(&page->_mapcount)) {
 		__inc_zone_page_state(page, NR_FILE_MAPPED);
-		mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
+		if (memcg)
+			mem_cgroup_inc_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
 	}
+	rcu_read_unlock();
+
 	mem_cgroup_end_update_page_stat(page, &locked, &flags);
 }
 
@@ -1129,14 +1141,22 @@ void page_remove_rmap(struct page *page)
 	bool anon = PageAnon(page);
 	bool locked;
 	unsigned long flags;
+	struct page_cgroup *pc;
+	struct mem_cgroup *memcg = NULL;
 
 	/*
 	 * The anon case has no mem_cgroup page_stat to update; but may
 	 * uncharge_page() below, where the lock ordering can deadlock if
 	 * we hold the lock against page_stat move: so avoid it on anon.
 	 */
-	if (!anon)
+	if (!anon) {
 		mem_cgroup_begin_update_page_stat(page, &locked, &flags);
+		pc = lookup_page_cgroup(page);
+		rcu_read_lock();
+		memcg = pc->mem_cgroup;
+		if (unlikely(!PageCgroupUsed(pc)))
+			memcg = NULL;
+	}
 
 	/* page still mapped by someone else? */
 	if (!atomic_add_negative(-1, &page->_mapcount))
@@ -1157,7 +1177,9 @@ void page_remove_rmap(struct page *page)
 					      NR_ANON_TRANSPARENT_HUGEPAGES);
 	} else {
 		__dec_zone_page_state(page, NR_FILE_MAPPED);
-		mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
+		if (memcg)
+			mem_cgroup_dec_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
+		rcu_read_unlock();
 		mem_cgroup_end_update_page_stat(page, &locked, &flags);
 	}
 	if (unlikely(PageMlocked(page)))
-- 
1.7.9.5

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