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Subject[RFC] [PATCH 9/9] memcg: percpu page cgroup lookup cache
Use per-cpu cache for fast access to page_cgroup.
This patch is for making fastpath faster.

Because page_cgroup is accessed when the page is allocated/freed,
we can assume several of continuous page_cgroup will be accessed soon.
(If not interleaved on NUMA...but in such case, alloc/free itself is slow.)

We cache some set of page_cgroup's base pointer on per-cpu area and
use it when we hit.

TODO:
- memory/cpu hotplug support.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

---
mm/page_cgroup.c | 47 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 45 insertions(+), 2 deletions(-)
Index: mmtom-2.6.27-rc5+/mm/page_cgroup.c
===================================================================
--- mmtom-2.6.27-rc5+.orig/mm/page_cgroup.c
+++ mmtom-2.6.27-rc5+/mm/page_cgroup.c
@@ -57,14 +57,26 @@ static int pcg_hashmask __read_mostly;
#define PCG_HASHMASK (pcg_hashmask)
#define PCG_HASHSIZE (1 << pcg_hashshift)

+#define PCG_CACHE_MAX_SLOT (32)
+#define PCG_CACHE_MASK (PCG_CACHE_MAX_SLOT - 1)
+struct percpu_page_cgroup_cache {
+ struct {
+ unsigned long index;
+ struct page_cgroup *base;
+ } slots[PCG_CACHE_MAX_SLOT];
+};
+DEFINE_PER_CPU(struct percpu_page_cgroup_cache, pcg_cache);
+
int pcg_hashfun(unsigned long index)
{
return hash_long(index, pcg_hashshift);
}

-struct page_cgroup *lookup_page_cgroup(unsigned long pfn)
+noinline static struct page_cgroup *
+__lookup_page_cgroup(struct percpu_page_cgroup_cache *pcc,unsigned long pfn)
{
unsigned long index = pfn >> ENTS_PER_CHUNK_SHIFT;
+ int s = index & PCG_CACHE_MASK;
struct pcg_hash *ent;
struct pcg_hash_head *head;
struct hlist_node *node;
@@ -77,6 +89,8 @@ struct page_cgroup *lookup_page_cgroup(u
hlist_for_each_entry(ent, node, &head->head, node) {
if (ent->index == index) {
pc = ent->map + pfn;
+ pcc->slots[s].index = ent->index;
+ pcc->slots[s].base = ent->map;
break;
}
}
@@ -84,6 +98,22 @@ struct page_cgroup *lookup_page_cgroup(u
return pc;
}

+struct page_cgroup *lookup_page_cgroup(unsigned long pfn)
+{
+ unsigned long index = pfn >> ENTS_PER_CHUNK_SHIFT;
+ int hnum = (pfn >> ENTS_PER_CHUNK_SHIFT) & PCG_CACHE_MASK;
+ struct percpu_page_cgroup_cache *pcc;
+ struct page_cgroup *ret;
+
+ pcc = &get_cpu_var(pcg_cache);
+ if (likely(pcc->slots[hnum].index == index))
+ ret = pcc->slots[hnum].base + pfn;
+ else
+ ret = __lookup_page_cgroup(pcc, pfn);
+ put_cpu_var(pcg_cache);
+ return ret;
+}
+
static void __meminit alloc_page_cgroup(int node, unsigned long index)
{
struct pcg_hash *ent;
@@ -124,12 +154,23 @@ static void __meminit alloc_page_cgroup(
return;
}

+void clear_page_cgroup_cache_pcg(int cpu)
+{
+ struct percpu_page_cgroup_cache *pcc;
+ int i;
+
+ pcc = &per_cpu(pcg_cache, cpu);
+ for (i = 0; i < PCG_CACHE_MAX_SLOT; i++) {
+ pcc->slots[i].index = -1;
+ pcc->slots[i].base = NULL;
+ }
+}

/* Called From mem_cgroup's initilization */
void __init page_cgroup_init(void)
{
struct pcg_hash_head *head;
- int node, i;
+ int node, cpu, i;
unsigned long start, pfn, end, index, offset;
long default_pcg_hash_size;

@@ -174,5 +215,7 @@ void __init page_cgroup_init(void)
}
}
}
+ for_each_possible_cpu(cpu)
+ clear_page_cgroup_cache_pcg(cpu);
return;
}


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