Just a "heads up":  This patch is the apparent cause of a boot time
panic--null pointer deref--on my numa platform.  See below.

On Tue, 2007-11-27 at 12:00 +0900, KAMEZAWA Hiroyuki wrote:
> Counting active/inactive per-zone in memory controller.
> 
> This patch adds per-zone status in memory cgroup.
> These values are often read (as per-zone value) by page reclaiming.
> 
> In current design, per-zone stat is just a unsigned long value and 
> not an atomic value because they are modified only under lru_lock.
> (So, atomic_ops is not necessary.)
> 
> This patch adds ACTIVE and INACTIVE per-zone status values.
> 
> For handling per-zone status, this patch adds
>   struct mem_cgroup_per_zone {
> 		...
>   }
> and some helper functions. This will be useful to add per-zone objects
> in mem_cgroup.
> 
> This patch turns memory controller's early_init to be 0 for calling 
> kmalloc() in initialization.
> 
> Changelog V2 -> V3
>   - fixed comments.
> 
> Changelog V1 -> V2
>   - added mem_cgroup_per_zone struct.
>       This will help following patches to implement per-zone objects and
>       pack them into a struct.
>   - added __mem_cgroup_add_list() and __mem_cgroup_remove_list()
>   - fixed page migration handling.
>   - renamed zstat to info (per-zone-info)
>     This will be place for per-zone information(lru, lock, ..)
>   - use page_cgroup_nid()/zid() funcs.
> 
> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> 
>  mm/memcontrol.c |  164 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 157 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6.24-rc3-mm1/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.24-rc3-mm1.orig/mm/memcontrol.c	2007-11-26 16:39:00.000000000 +0900
> +++ linux-2.6.24-rc3-mm1/mm/memcontrol.c	2007-11-26 16:39:02.000000000 +0900
> @@ -78,6 +78,31 @@
<snip>
>  
> +static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
> +{
> +	struct mem_cgroup_per_node *pn;
> +
> +	pn = kmalloc_node(sizeof(*pn), GFP_KERNEL, node);
> +	if (!pn)
> +		return 1;
> +	mem->info.nodeinfo[node] = pn;
> +	memset(pn, 0, sizeof(*pn));
> +	return 0;
> +}
> +
>  static struct mem_cgroup init_mem_cgroup;
>  
>  static struct cgroup_subsys_state *
>  mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  {
>  	struct mem_cgroup *mem;
> +	int node;
>  
>  	if (unlikely((cont->parent) == NULL)) {
>  		mem = &init_mem_cgroup;
> @@ -907,7 +1039,19 @@
>  	INIT_LIST_HEAD(&mem->inactive_list);
>  	spin_lock_init(&mem->lru_lock);
>  	mem->control_type = MEM_CGROUP_TYPE_ALL;
> +	memset(&mem->info, 0, sizeof(mem->info));
> +
> +	for_each_node_state(node, N_POSSIBLE)
> +		if (alloc_mem_cgroup_per_zone_info(mem, node))
> +			goto free_out;
> +

As soon as this loop hits the first non-existent node on my platform, I
get a NULL pointer deref down in __alloc_pages.  Stack trace below.

Perhaps N_POSSIBLE should be N_HIGH_MEMORY?  That would require handling
of memory/node hotplug for each memory control group, right?  But, I'm
going to try N_HIGH_MEMORY as a work around.

Lee
>  	return &mem->css;
> +free_out:
> +	for_each_node_state(node, N_POSSIBLE)
> +		kfree(mem->info.nodeinfo[node]);
> +	if (cont->parent != NULL)
> +		kfree(mem);
> +	return NULL;
>  }
>  
>  static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
> @@ -920,6 +1064,12 @@
>  static void mem_cgroup_destroy(struct cgroup_subsys *ss,
>  				struct cgroup *cont)
>  {
> +	int node;
> +	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> +
> +	for_each_node_state(node, N_POSSIBLE)
> +		kfree(mem->info.nodeinfo[node]);
> +
>  	kfree(mem_cgroup_from_cont(cont));
>  }
>  
> @@ -972,5 +1122,5 @@
>  	.destroy = mem_cgroup_destroy,
>  	.populate = mem_cgroup_populate,
>  	.attach = mem_cgroup_move_task,
> -	.early_init = 1,
> +	.early_init = 0,
>  };

Initializing cgroup subsys memory
Unable to handle kernel NULL pointer dereference (address 0000000000003c80)
swapper[0]: Oops 11012296146944 [1]
Modules linked in:

Pid: 0, CPU 0, comm:              swapper
psr : 00001210084a6010 ifs : 8000000000000b1a ip  : [<a000000100132e11>]    Not tainted
ip is at __alloc_pages+0x31/0x6e0
unat: 0000000000000000 pfs : 000000000000060f rsc : 0000000000000003
rnat: a0000001009db3b8 bsps: a0000001009e0490 pr  : 656960155aa65659
ldrs: 0000000000000000 ccv : 0000000000000000 fpsr: 0009804c8a70433f
csd : 0000000000000000 ssd : 0000000000000000
b0  : a000000100187370 b6  : a000000100194440 b7  : a00000010086d560
f6  : 1003e0000000000000000 f7  : 1003e0000000000000055
f8  : 1003e00000000000000c0 f9  : 1003e0000000000003fc0
f10 : 1003e00000000000000c0 f11 : 1003e0000000000000055
r1  : a000000100bc0f10 r2  : ffffffffffe00006 r3  : 0000000000020000
r8  : 0000000000071ef0 r9  : 0000000000000005 r10 : e00007002034d588
r11 : e00007002034d580 r12 : a0000001008e3df0 r13 : a0000001008dc000
r14 : 0000000000000001 r15 : e00007002034d5b0 r16 : 0000000000001e78
r17 : ffffffffffff04e0 r18 : 0000000000100002 r19 : 0000000000000000
r20 : 0000000000100002 r21 : 00000000000003cf r22 : 000000000000000f
r23 : 00000000000003c0 r24 : 0000000000000010 r25 : 0000000000000001
r26 : a0000001008e3e20 r27 : 0000000000000000 r28 : e0000701813dc088
r29 : e0000701813dc080 r30 : 0000000000000000 r31 : a000000100918ea8

Call Trace:
 [<a000000100014de0>] show_stack+0x80/0xa0
                                sp=a0000001008e39c0 bsp=a0000001008dd1b0
 [<a000000100015a70>] show_regs+0x870/0x8a0
                                sp=a0000001008e3b90 bsp=a0000001008dd158
 [<a00000010003d130>] die+0x190/0x300
                                sp=a0000001008e3b90 bsp=a0000001008dd110
 [<a000000100071b80>] ia64_do_page_fault+0x8e0/0xa20
                                sp=a0000001008e3b90 bsp=a0000001008dd0b8
 [<a00000010000b5c0>] ia64_leave_kernel+0x0/0x270
                                sp=a0000001008e3c20 bsp=a0000001008dd0b8
 [<a000000100132e10>] __alloc_pages+0x30/0x6e0
                                sp=a0000001008e3df0 bsp=a0000001008dcfe0
 [<a000000100187370>] new_slab+0x610/0x6c0
                                sp=a0000001008e3e00 bsp=a0000001008dcf80
 [<a000000100187470>] get_new_slab+0x50/0x200
                                sp=a0000001008e3e00 bsp=a0000001008dcf48
 [<a000000100187900>] __slab_alloc+0x2e0/0x4e0
                                sp=a0000001008e3e00 bsp=a0000001008dcf00
 [<a000000100187c80>] kmem_cache_alloc_node+0x180/0x200
                                sp=a0000001008e3e10 bsp=a0000001008dcec0
 [<a0000001001945a0>] mem_cgroup_create+0x160/0x400
                                sp=a0000001008e3e10 bsp=a0000001008dce78
 [<a0000001000f0940>] cgroup_init_subsys+0xa0/0x400
                                sp=a0000001008e3e20 bsp=a0000001008dce28
 [<a0000001008521f0>] cgroup_init+0x90/0x160
                                sp=a0000001008e3e20 bsp=a0000001008dce00
 [<a000000100831960>] start_kernel+0x700/0x820
                                sp=a0000001008e3e20 bsp=a0000001008dcd80



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