On Mon, 2010-05-24 at 09:03 +0800, Guo, Chaohong wrote:
>
> >> >>
> >> >>
> >> >> @@ -2968,9 +2991,23 @@ static int __build_all_zonelists(void *d
> >> >> ...
> >> >>
> >> >> - for_each_possible_cpu(cpu)
> >> >> + for_each_possible_cpu(cpu) {
> >> >> setup_pageset(&per_cpu(boot_pageset, cpu), 0);
> >> >> ...
> >> >>
> >> >> +#ifdef CONFIG_HAVE_MEMORYLESS_NODES
> >> >> + if (cpu_online(cpu))
> >> >> + cpu_to_mem(cpu) = local_memory_node(cpu_to_node(cpu));
> >> >> +#endif
> >>
> >> Look at the above code, int __build_all_zonelists(), cpu_to_mem(cpu)
> >> is set only when cpu is onlined. Suppose that a node with local memory,
> >> all memory segments are onlined first, and then, cpus within that node
> >> are onlined one by one, in this case, where does the cpu_to_mem(cpu)
> >> for the last cpu get its value ?
> >
> >Minskey:
> >
> >As I mentioned to Kame-san, x86 does not define
> >CONFIG_HAVE_MEMORYLESS_NODES, so this code is not compiled for that
> >arch. If x86 did support memoryless nodes--i.e., did not hide them and
> >reassign the cpus to other nodes, as is the case for ia64--then we could
> >have on-line cpus associated with memoryless nodes. The code above is
> >in __build_all_zonelists() so that in the case where we add memory to a
> >previously memoryless node, we re-evaluate the "local memory node" for
> >all online cpus.
> >
> >For cpu hotplug--again, if x86 supports memoryless nodes--we'll need to
> >add a similar chunk to the path where we set up the cpu_to_node map for
> >a hotplugged cpu. See, for example, the call to set_numa_mem() in
> >smp_callin() in arch/ia64/kernel/smpboot.c.
>
>
> Yeah, that's what I am looking for.
>
>
>
> But currently, I don't
> >think you can use the numa_mem_id()/cpu_to_mem() interfaces for your
> >purpose. I suppose you could change page_alloc.c to compile
> >local_memory_node() #if defined(CONFIG_HAVE_MEMORYLESS_NODES) ||
> >defined
> >(CPU_HOTPLUG) and use that function to find the nearest memory. It
> >should return a valid node after zonelists have been rebuilt.
> >
> >Does that make sense?
>
> Yes, besides, I need to find a place in hotplug path to call set_numa_mem()
> just as you mentioned for ia64 platform. Is my understanding right ?
I don't think you can use any of the "numa_mem" functions on x86[_64]
without doing a lot more work to expose memoryless nodes. On x86_64,
numa_mem_id() and cpu_to_mem() always return the same as numa_node_id()
and cpu_to_node(). This is because x86_64 code hides memoryless nodes
and reassigns all cpus to nodes with memory. Are you planning on
changing this such that memoryless nodes remain on-line with their cpus
associated with them? If so, go for it! If not, then you don't need
to [can't really, I think] use set_numa_mem()/cpu_to_mem() for your
purposes. That's why I suggested you arrange for local_memory_node() to
be compiled for CPU_HOTPLUG and call that function directly to obtain a
nearby node from which you can allocate memory during cpu hot plug. Or,
I could just completely misunderstand what you propose to do with these
percpu variables.
Lee
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>