[RFC][PATCH 1/3] memcg: add methods to access pc->mem_cgroup

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

In order to encode pc->mem_cgroup and pc->flags to be in a word,
access function to pc->mem_cgroup is required.

This patch replaces access to pc->mem_cgroup with
 pc_to_mem_cgroup(pc)          : pc->mem_cgroup
 pc_set_mem_cgroup(pc, memcg)  : pc->mem_cgroup = memcg

Following patch will remove pc->mem_cgroup.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 include/linux/page_cgroup.h |   12 +++++++
 mm/memcontrol.c             |   69 ++++++++++++++++++++++--------------------
 2 files changed, 48 insertions(+), 33 deletions(-)

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index a88cdba..92768cb 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -82,6 +82,18 @@ static inline void unlock_page_cgroup(struct page_cgroup *pc)
 	bit_spin_unlock(PCG_LOCK, &pc->flags);
 }
 
+
+static inline struct mem_cgroup* pc_to_mem_cgroup(struct page_cgroup *pc)
+{
+	return pc->mem_cgroup;
+}
+
+static inline void
+pc_set_mem_cgroup(struct page_cgroup *pc, struct mem_cgroup *memcg)
+{
+	pc->mem_cgroup = memcg;
+}
+
 #else /* CONFIG_CGROUP_MEM_RES_CTLR */
 struct page_cgroup;
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c65e6bc..124fec9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1014,9 +1014,9 @@ struct lruvec *mem_cgroup_zone_lruvec(struct zone *zone,
 /*
  * Following LRU functions are allowed to be used without PCG_LOCK.
  * Operations are called by routine of global LRU independently from memcg.
- * What we have to take care of here is validness of pc->mem_cgroup.
+ * What we have to take care of here is validness of pc's mem_cgroup.
  *
- * Changes to pc->mem_cgroup happens when
+ * Changes to pc's mem_cgroup happens when
  * 1. charge
  * 2. moving account
  * In typical case, "charge" is done before add-to-lru. Exception is SwapCache.
@@ -1048,7 +1048,7 @@ struct lruvec *mem_cgroup_lru_add_list(struct zone *zone, struct page *page,
 		return &zone->lruvec;
 
 	pc = lookup_page_cgroup(page);
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 
 	/*
 	 * Surreptitiously switch any uncharged page to root:
@@ -1057,10 +1057,12 @@ struct lruvec *mem_cgroup_lru_add_list(struct zone *zone, struct page *page,
 	 *
 	 * Our caller holds lru_lock, and PageCgroupUsed is updated
 	 * under page_cgroup lock: between them, they make all uses
-	 * of pc->mem_cgroup safe.
+	 * of pc's mem_cgroup safe.
 	 */
-	if (!PageCgroupUsed(pc) && memcg != root_mem_cgroup)
-		pc->mem_cgroup = memcg = root_mem_cgroup;
+	if (!PageCgroupUsed(pc) && memcg != root_mem_cgroup) {
+		pc_set_mem_cgroup(pc, root_mem_cgroup);
+		memcg = root_mem_cgroup;
+	}
 
 	mz = page_cgroup_zoneinfo(memcg, page);
 	/* compound_order() is stabilized through lru_lock */
@@ -1088,7 +1090,7 @@ void mem_cgroup_lru_del_list(struct page *page, enum lru_list lru)
 		return;
 
 	pc = lookup_page_cgroup(page);
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 	VM_BUG_ON(!memcg);
 	mz = page_cgroup_zoneinfo(memcg, page);
 	/* huge page split is done under lru_lock. so, we have no races. */
@@ -1235,9 +1237,9 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
 	pc = lookup_page_cgroup(page);
 	if (!PageCgroupUsed(pc))
 		return NULL;
-	/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
+	/* Ensure pc's mem_cgroup is visible after reading PCG_USED. */
 	smp_rmb();
-	mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
+	mz = page_cgroup_zoneinfo(pc_to_mem_cgroup(pc), page);
 	return &mz->reclaim_stat;
 }
 
@@ -1314,7 +1316,7 @@ static void mem_cgroup_end_move(struct mem_cgroup *memcg)
  *
  * mem_cgroup_stolen() -  checking whether a cgroup is mc.from or not. This
  *			  is used for avoiding races in accounting.  If true,
- *			  pc->mem_cgroup may be overwritten.
+ *			  pc's mem_cgroup may be overwritten.
  *
  * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
  *			  under hierarchy of moving cgroups. This is for
@@ -1887,8 +1889,8 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *memcg, gfp_t mask)
  * file-stat operations happen after a page is attached to radix-tree. There
  * are no race with "charge".
  *
- * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
- * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
+ * Considering "uncharge", we know that memcg doesn't clear pc's mem_cgroup
+ * at "uncharge" intentionally. So, we always see valid pc's mem_cgroup even
  * if there are race with "uncharge". Statistics itself is properly handled
  * by flags.
  *
@@ -1905,7 +1907,7 @@ void __mem_cgroup_begin_update_page_stat(struct page *page,
 
 	pc = lookup_page_cgroup(page);
 again:
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 	if (unlikely(!memcg || !PageCgroupUsed(pc)))
 		return;
 	/*
@@ -1918,7 +1920,7 @@ again:
 		return;
 
 	move_lock_mem_cgroup(memcg, flags);
-	if (memcg != pc->mem_cgroup || !PageCgroupUsed(pc)) {
+	if (memcg != pc_to_mem_cgroup(pc) || !PageCgroupUsed(pc)) {
 		move_unlock_mem_cgroup(memcg, flags);
 		goto again;
 	}
@@ -1930,11 +1932,11 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
 	struct page_cgroup *pc = lookup_page_cgroup(page);
 
 	/*
-	 * It's guaranteed that pc->mem_cgroup never changes while
-	 * lock is held because a routine modifies pc->mem_cgroup
+	 * It's guaranteed that pc's mem_cgroup never changes while
+	 * lock is held because a routine modifies pc's mem_cgroup
 	 * should take move_lock_page_cgroup().
 	 */
-	move_unlock_mem_cgroup(pc->mem_cgroup, flags);
+	move_unlock_mem_cgroup(pc_to_mem_cgroup(pc), flags);
 }
 
 void mem_cgroup_update_page_stat(struct page *page,
@@ -1947,7 +1949,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 	if (mem_cgroup_disabled())
 		return;
 
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 	if (unlikely(!memcg || !PageCgroupUsed(pc)))
 		return;
 
@@ -2244,7 +2246,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
  * has TIF_MEMDIE, this function returns -EINTR while writing root_mem_cgroup
  * to *ptr. There are two reasons for this. 1: fatal threads should quit as soon
  * as possible without any hazards. 2: all pages should have a valid
- * pc->mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
+ * pc's mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
  * pointer, that is treated as a charge to root_mem_cgroup.
  *
  * So __mem_cgroup_try_charge() will return
@@ -2437,7 +2439,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 	pc = lookup_page_cgroup(page);
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
-		memcg = pc->mem_cgroup;
+		memcg = pc_to_mem_cgroup(pc);
 		if (memcg && !css_tryget(&memcg->css))
 			memcg = NULL;
 	} else if (PageSwapCache(page)) {
@@ -2489,11 +2491,11 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
 		}
 	}
 
-	pc->mem_cgroup = memcg;
+	pc_set_mem_cgroup(pc, memcg);
 	/*
 	 * We access a page_cgroup asynchronously without lock_page_cgroup().
-	 * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
-	 * is accessed after testing USED bit. To make pc->mem_cgroup visible
+	 * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
+	 * is accessed after testing USED bit. To make pc's mem_cgroup visible
 	 * before USED bit, we need memory barrier here.
 	 * See mem_cgroup_add_lru_list(), etc.
  	 */
@@ -2538,13 +2540,14 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 {
 	struct page_cgroup *head_pc = lookup_page_cgroup(head);
 	struct page_cgroup *pc;
+	struct mem_cgroup *memcg = pc_to_mem_cgroup(head_pc);
 	int i;
 
 	if (mem_cgroup_disabled())
 		return;
 	for (i = 1; i < HPAGE_PMD_NR; i++) {
 		pc = head_pc + i;
-		pc->mem_cgroup = head_pc->mem_cgroup;
+		pc_set_mem_cgroup(pc, memcg);
 		smp_wmb();/* see __commit_charge() */
 		pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
 	}
@@ -2595,7 +2598,7 @@ static int mem_cgroup_move_account(struct page *page,
 	lock_page_cgroup(pc);
 
 	ret = -EINVAL;
-	if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
+	if (!PageCgroupUsed(pc) || pc_to_mem_cgroup(pc) != from)
 		goto unlock;
 
 	move_lock_mem_cgroup(from, &flags);
@@ -2613,7 +2616,7 @@ static int mem_cgroup_move_account(struct page *page,
 		__mem_cgroup_cancel_charge(from, nr_pages);
 
 	/* caller should have done css_get */
-	pc->mem_cgroup = to;
+	pc_set_mem_cgroup(pc, to);
 	mem_cgroup_charge_statistics(to, anon, nr_pages);
 	/*
 	 * We charges against "to" which may not have any tasks. Then, "to"
@@ -2956,7 +2959,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
 	lock_page_cgroup(pc);
 
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 
 	if (!PageCgroupUsed(pc))
 		goto unlock_out;
@@ -2992,7 +2995,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 
 	ClearPageCgroupUsed(pc);
 	/*
-	 * pc->mem_cgroup is not cleared here. It will be accessed when it's
+	 * pc's mem_cgroup is not cleared here. It will be accessed when it's
 	 * freed from LRU. This is safe because uncharged page is expected not
 	 * to be reused (freed soon). Exception is SwapCache, it's handled by
 	 * special functions.
@@ -3214,7 +3217,7 @@ int mem_cgroup_prepare_migration(struct page *page,
 	pc = lookup_page_cgroup(page);
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
-		memcg = pc->mem_cgroup;
+		memcg = pc_to_mem_cgroup(pc);
 		css_get(&memcg->css);
 		/*
 		 * At migrating an anonymous page, its mapcount goes down
@@ -3359,7 +3362,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
 	pc = lookup_page_cgroup(oldpage);
 	/* fix accounting on old pages */
 	lock_page_cgroup(pc);
-	memcg = pc->mem_cgroup;
+	memcg = pc_to_mem_cgroup(pc);
 	mem_cgroup_charge_statistics(memcg, false, -1);
 	ClearPageCgroupUsed(pc);
 	unlock_page_cgroup(pc);
@@ -3370,7 +3373,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
 	/*
 	 * Even if newpage->mapping was NULL before starting replacement,
 	 * the newpage may be on LRU(or pagevec for LRU) already. We lock
-	 * LRU while we overwrite pc->mem_cgroup.
+	 * LRU while we overwrite pc's mem_cgroup.
 	 */
 	__mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true);
 }
@@ -3406,7 +3409,7 @@ void mem_cgroup_print_bad_page(struct page *page)
 	pc = lookup_page_cgroup_used(page);
 	if (pc) {
 		printk(KERN_ALERT "pc:%p pc->flags:%lx pc->mem_cgroup:%p\n",
-		       pc, pc->flags, pc->mem_cgroup);
+		       pc, pc->flags, pc_to_mem_cgroup(pc));
 	}
 }
 #endif
@@ -5197,7 +5200,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
 		 * mem_cgroup_move_account() checks the pc is valid or not under
 		 * the lock.
 		 */
-		if (PageCgroupUsed(pc) && pc->mem_cgroup == mc.from) {
+		if (PageCgroupUsed(pc) && pc_to_mem_cgroup(pc) == mc.from) {
 			ret = MC_TARGET_PAGE;
 			if (target)
 				target->page = page;
-- 
1.7.4.1


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