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From: KAMEZAWA Hiroyuki on 2 Aug 2010 06:20
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>

Now, memory cgroup has an ID per cgroup and make use of it at
- hierarchy walk,
- swap recording.

This patch is for making more use of it. The final purpose is
to replace page_cgroup->mem_cgroup's pointer to an unsigned short.

This patch caches a pointer of memcg in an array. By this, we
don't have to call css_lookup() which requires radix-hash walk.
This saves some amount of memory footprint at lookup memcg via id.

Changelog: 20100730
- fixed rcu_read_unlock() placement.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
---
init/Kconfig | 11 +++++++++++
mm/memcontrol.c | 48 ++++++++++++++++++++++++++++++++++--------------
2 files changed, 45 insertions(+), 14 deletions(-)

Index: mmotm-0727/mm/memcontrol.c
===================================================================
--- mmotm-0727.orig/mm/memcontrol.c
+++ mmotm-0727/mm/memcontrol.c
@@ -292,6 +292,30 @@ static bool move_file(void)
&mc.to->move_charge_at_immigrate);
}

+/* 0 is unused */
+static atomic_t mem_cgroup_num;
+#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
+static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
+
+static struct mem_cgroup *id_to_memcg(unsigned short id)
+{
+ /*
+ * This array is set to NULL when mem_cgroup is freed.
+ * IOW, there are no more references && rcu_synchronized().
+ * This lookup-caching is safe.
+ */
+ if (unlikely(!mem_cgroups[id])) {
+ struct cgroup_subsys_state *css;
+
+ rcu_read_lock();
+ css = css_lookup(&mem_cgroup_subsys, id);
+ rcu_read_unlock();
+ if (!css)
+ return NULL;
+ mem_cgroups[id] = container_of(css, struct mem_cgroup, css);
+ }
+ return mem_cgroups[id];
+}
/*
* Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
* limit reclaim to prevent infinite loops, if they ever occur.
@@ -1824,18 +1848,7 @@ static void mem_cgroup_cancel_charge(str
* it's concern. (dropping refcnt from swap can be called against removed
* memcg.)
*/
-static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
-{
- struct cgroup_subsys_state *css;

- /* ID 0 is unused ID */
- if (!id)
- return NULL;
- css = css_lookup(&mem_cgroup_subsys, id);
- if (!css)
- return NULL;
- return container_of(css, struct mem_cgroup, css);
-}

struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
@@ -1856,7 +1869,7 @@ struct mem_cgroup *try_get_mem_cgroup_fr
ent.val = page_private(page);
id = lookup_swap_cgroup(ent);
rcu_read_lock();
- mem = mem_cgroup_lookup(id);
+ mem = id_to_memcg(id);
if (mem && !css_tryget(&mem->css))
mem = NULL;
rcu_read_unlock();
@@ -2208,7 +2221,7 @@ __mem_cgroup_commit_charge_swapin(struct

id = swap_cgroup_record(ent, 0);
rcu_read_lock();
- memcg = mem_cgroup_lookup(id);
+ memcg = id_to_memcg(id);
if (memcg) {
/*
* This recorded memcg can be obsolete one. So, avoid
@@ -2472,7 +2485,7 @@ void mem_cgroup_uncharge_swap(swp_entry_

id = swap_cgroup_record(ent, 0);
rcu_read_lock();
- memcg = mem_cgroup_lookup(id);
+ memcg = id_to_memcg(id);
if (memcg) {
/*
* We uncharge this because swap is freed.
@@ -3988,6 +4001,9 @@ static struct mem_cgroup *mem_cgroup_all
struct mem_cgroup *mem;
int size = sizeof(struct mem_cgroup);

+ if (atomic_read(&mem_cgroup_num) == NR_MEMCG_GROUPS)
+ return NULL;
+
/* Can be very big if MAX_NUMNODES is very big */
if (size < PAGE_SIZE)
mem = kmalloc(size, GFP_KERNEL);
@@ -4025,7 +4041,10 @@ static void __mem_cgroup_free(struct mem
int node;

mem_cgroup_remove_from_trees(mem);
+ /* No more lookup against this ID */
+ mem_cgroups[css_id(&mem->css)] = NULL;
free_css_id(&mem_cgroup_subsys, &mem->css);
+ atomic_dec(&mem_cgroup_num);

for_each_node_state(node, N_POSSIBLE)
free_mem_cgroup_per_zone_info(mem, node);
@@ -4162,6 +4181,7 @@ mem_cgroup_create(struct cgroup_subsys *
atomic_set(&mem->refcnt, 1);
mem->move_charge_at_immigrate = 0;
mutex_init(&mem->thresholds_lock);
+ atomic_inc(&mem_cgroup_num);
return &mem->css;
free_out:
__mem_cgroup_free(mem);
Index: mmotm-0727/init/Kconfig
===================================================================
--- mmotm-0727.orig/init/Kconfig
+++ mmotm-0727/init/Kconfig
@@ -594,6 +594,17 @@ config CGROUP_MEM_RES_CTLR_SWAP
Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
size is 4096bytes, 512k per 1Gbytes of swap.

+config MEM_CGROUP_MAX_GROUPS
+ int "Maximum number of memory cgroups on a system"
+ range 1 65535
+ default 8192 if 64BIT
+ default 2048 if 32BIT
+ help
+ Memory cgroup has limitation of the number of groups created.
+ Please select your favorite value. The more you allow, the more
+ memory will be consumed. This consumes vmalloc() area, so,
+ this should be small on 32bit arch.
+
menuconfig CGROUP_SCHED
bool "Group CPU scheduler"
depends on EXPERIMENTAL && CGROUPS

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