Re: [Bugme-new] [Bug 36192] New: Kernel panic when boot the 2.6.39+ kernel based off of 2.6.32 kernel

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Jun 08, 2011 at 08:45:38AM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 7 Jun 2011 12:26:11 +0200
> Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
> > On Tue, Jun 07, 2011 at 04:55:37PM +0900, KAMEZAWA Hiroyuki wrote:
> > > On Tue, 7 Jun 2011 09:51:31 +0200
> > > Johannes Weiner <hannes@cmpxchg.org> wrote:
> > > > @@ -283,23 +285,30 @@ static int __meminit page_cgroup_callback(struct notifier_block *self,
> > > >  
> > > >  void __init page_cgroup_init(void)
> > > >  {
> > > > -	unsigned long pfn;
> > > > -	int fail = 0;
> > > > +	pg_data_t *pgdat;
> > > >  
> > > >  	if (mem_cgroup_disabled())
> > > >  		return;
> > > >  
> > > > -	for (pfn = 0; !fail && pfn < max_pfn; pfn += PAGES_PER_SECTION) {
> > > > -		if (!pfn_present(pfn))
> > > > -			continue;
> > > > -		fail = init_section_page_cgroup(pfn);
> > > > -	}
> > > > -	if (fail) {
> > > > -		printk(KERN_CRIT "try 'cgroup_disable=memory' boot option\n");
> > > > -		panic("Out of memory");
> > > > -	} else {
> > > > -		hotplug_memory_notifier(page_cgroup_callback, 0);
> > > > +	for_each_online_pgdat(pgdat) {
> > > > +		unsigned long start;
> > > > +		unsigned long end;
> > > > +		unsigned long pfn;
> > > > +
> > > > +		start = pgdat->node_start_pfn & ~(PAGES_PER_SECTION - 1);
> > > > +		end = ALIGN(pgdat->node_start_pfn + pgdat->node_spanned_pages,
> > > > +			    PAGES_PER_SECTION);
> > > > +		for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
> > > > +			if (!pfn_present(pfn))
> > > > +				continue;
> > > > +			if (!init_section_page_cgroup(pgdat->node_id, pfn))
> > > > +				continue;
> > > 
> > > AFAIK, nodes can overlap. So, this [start, end) scan doesn't work. sections
> > > may be initizalised mulitple times ...in wrong way. At here, what we can trust
> > > is nid in page->flags or early_node_map[]?.
> > 
> > Sections are not be initialized multiple times.  Once their
> > page_cgroup array is allocated they are skipped if considered again
> > later.
> > 
> > Second, even if there are two nodes backing the memory of a single
> > section, there is still just a single page_cgroup array per section,
> > we have to take the memory from one node or the other.
> > 
> > So if both node N1 and N2 fall into section SN, SN->page_cgroup will
> > be an array of page_cgroup structures, allocated on N1, to represent
> > the pages of SN.
> > 
> > The first section considered when walking the PFNs of N2 will be SN,
> > which will be skipped because of !!SN->page_cgroup.
> > 
> > I do not see the problem.
> > 
> 
> Assume a host with node layout
> 
> N0 | N1 | N2 | N3 | N4 | N0
> 
> 
> pages for all node will be allocated onto node-0.

That makes sense, thanks for the explanation!

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