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Subject[RFC][PATCH 2/6] memcg: add pc_set_mem_cgroup_and_flags()
Consolidate a code for setting pc->mem_cgroup and USED bit which requires smp_wmb().
And remove a macro PCGF_NOCOPY_AT_SPLIT which isn't helpful to read code, now.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/page_cgroup.h | 18 ++++++++++++++++++
mm/memcontrol.c | 18 ++++--------------
2 files changed, 22 insertions(+), 14 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 92768cb..2707809 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -1,6 +1,8 @@
#ifndef __LINUX_PAGE_CGROUP_H
#define __LINUX_PAGE_CGROUP_H

+#include <linux/smp.h>
+
enum {
/* flags for mem_cgroup */
PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
@@ -94,6 +96,22 @@ pc_set_mem_cgroup(struct page_cgroup *pc, struct mem_cgroup *memcg)
pc->mem_cgroup = memcg;
}

+static inline void
+pc_set_mem_cgroup_and_flags(struct page_cgroup *pc, struct mem_cgroup *memcg,
+ unsigned long flags)
+{
+ pc->mem_cgroup = memcg;
+ /*
+ * We access a page_cgroup asynchronously without lock_page_cgroup().
+ * 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.
+ */
+ smp_wmb();
+ pc->flags = flags;
+}
+
#else /* CONFIG_CGROUP_MEM_RES_CTLR */
struct page_cgroup;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8077460..d366b60 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2511,16 +2511,7 @@ static void __mem_cgroup_commit_charge(struct 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'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.
- */
- smp_wmb();
- SetPageCgroupUsed(pc);
+ pc_set_mem_cgroup_and_flags(pc, memcg, BIT(PCG_USED) | BIT(PCG_LOCK));

if (lrucare) {
if (was_on_lru) {
@@ -2549,7 +2540,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

-#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (1 << PCG_MIGRATION))
/*
* Because tail pages are not marked as "used", set it. We're under
* zone->lru_lock, 'splitting on pmd' and compound_lock.
@@ -2565,11 +2555,11 @@ void mem_cgroup_split_huge_fixup(struct page *head)

if (mem_cgroup_disabled())
return;
+ if (!PageCgroupUsed(head_pc))
+ return;
for (i = 1; i < HPAGE_PMD_NR; i++) {
pc = head_pc + i;
- pc_set_mem_cgroup(pc, memcg);
- smp_wmb();/* see __commit_charge() */
- pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
+ pc_set_mem_cgroup_and_flags(pc, memcg, BIT(PCG_USED));
}
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
--
1.7.4.1



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