lkml.org 
[lkml]   [2012]   [Mar]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC][[PATCH 4/6] memcg: remove mem_cgroup pointer from page_cgroup

This patch removes pc->mem_cgroup and merge the pointer into flags as

63 4 0
| pointer to memcg..........|flags|
After this, memory cgroup's overhead is 8(4)bytes per a page.

Changelog:
- added BUILD_BUG_ON()
- update comments in Kconfig

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/page_cgroup.h | 21 +++++++++------------
init/Kconfig | 2 +-
2 files changed, 10 insertions(+), 13 deletions(-)
diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 3f3b4ff..7e3a3c7 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -3,6 +3,10 @@

#include <linux/smp.h>

+/*
+ * These flags are encoded into low bits of unsigned long,
+ * ORed with a pointer to mem_cgroup.
+ */
enum {
/* flags for mem_cgroup */
PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
@@ -12,6 +16,8 @@ enum {
__NR_PCG_FLAGS,
};

+#define PCG_FLAGS_MASK ((1 << __NR_PCG_FLAGS) - 1)
+
#ifndef __GENERATING_BOUNDS_H
#include <generated/bounds.h>

@@ -27,7 +33,6 @@ enum {
*/
struct page_cgroup {
unsigned long flags;
- struct mem_cgroup *mem_cgroup;
};

void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat);
@@ -93,7 +98,7 @@ extern struct mem_cgroup* root_mem_cgroup;
static inline struct mem_cgroup* pc_to_mem_cgroup(struct page_cgroup *pc)
{
if (likely(!PageCgroupReset(pc)))
- return pc->mem_cgroup;
+ return (struct mem_cgroup*)(pc->flags & ~PCG_FLAGS_MASK);
return root_mem_cgroup;
}

@@ -101,16 +106,8 @@ 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;
+ BUILD_BUG_ON(__NR_PCG_FLAGS > 5); /* assume 32byte alignment. */
+ pc->flags = (unsigned long)memcg | flags;
}

#else /* CONFIG_CGROUP_MEM_RES_CTLR */
diff --git a/init/Kconfig b/init/Kconfig
index 6cfd71d..e0bfe92 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -651,7 +651,7 @@ config CGROUP_MEM_RES_CTLR

Note that setting this option increases fixed memory overhead
associated with each page of memory in the system. By this,
- 20(40)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
+ 4(8)bytes/PAGE_SIZE on 32(64)bit system will be occupied by memory
usage tracking struct at boot. Total amount of this is printed out
at boot.

--
1.7.4.1



\
 
 \ /
  Last update: 2012-03-28 13:03    [from the cache]
©2003-2011 Jasper Spaans