> On Fri, 12 Oct 2007, Yasunori Goto wrote:
>
> > > > + down_read(&slub_lock);
> > > > + list_for_each_entry(s, &slab_caches, list) {
> > > > + local_node = page_to_nid(virt_to_page(s));
> > > > + if (local_node == offline_node)
> > > > + /* This slub is on the offline node. */
> > > > + return -EBUSY;
> > > > + }
> > > > + up_read(&slub_lock);
> > >
> > > So this checks if the any kmem_cache structure is on the offlined node? If
> > > so then we cannot offline the node?
> >
> > Right. If slabs' migration is possible, here would be good place for
> > doing it. But, it is not possible (at least now).
>
> I think you can avoid this check. The kmem_cache structures are allocated
> from the kmalloc array. The check if the kmalloc slabs are empty will fail
> if kmem_cache structures still exist on the node.
Ah, Ok.
>
> > > > + * because the node is used by slub yet.
> > > > + */
> > >
> > > It may be clearer to say:
> > >
> > > "If nr_slabs > 0 then slabs still exist on the node that is going down.
> > > We were unable to free them so we must fail."
> >
> > Again. If nr_slabs > 0, offline_pages must be fail due to slabs
> > remaining on the node before. So, this callback isn't called.
>
> Ok then we can remove these checks?
Hmm. Yes. I'll remove it.
>
> > > > +static int slab_mem_going_online_callback(void *arg)
> > > > +{
> > > > + struct kmem_cache_node *n;
> > > > + struct kmem_cache *s;
> > > > + struct memory_notify *marg = arg;
> > > > + int nid = marg->status_change_nid;
> > > > +
> > > > + /* If the node already has memory, then nothing is necessary. */
> > > > + if (nid < 0)
> > > > + return 0;
> > >
> > > The node must have memory???? Or we have already brought up the code?
> >
> > kmem_cache_node is created at boot time if the node has memory.
> > (Or, it is created by this callback on first added memory on the node).
> >
> > When nid = - 1, kmem_cache_node is created before this node due to
> > node has memory.
>
> So the function can be called for a node that is already online?
already "node memory available", accurately ;-)
>
> > > > + * New memory will be onlined on the node which has no memory so far.
> > > > + * New kmem_cache_node is necssary for it.
> > >
> > > "We are bringing a node online. No memory is available yet. We must
> > > allocate a kmem_cache_node structure in order to bring the node online." ?
> >
> > Your mention might be ok.
> > But. I would like to prefer to define status of node hotplug for
> > exactitude like followings
> >
> >
> > A)Node online -- pgdat is created and can be accessed for this node.
> > but there are no gurantee that cpu or memory is onlined.
> > This status is very close from memory-less node.
> > But this might be halfway status for node hotplug.
> > Node online bit is set. But N_HIGH_MEMORY
> > (or N_NORMAL_MEMORY) might be not set.
>
> Ahh.. Okay.
>
> > B)Node has memory--
> > one or more sections memory is onlined on the node.
> > N_HIGH_MEMORY (or N_NORMAL_MEMORY) is set.
> >
> > If first memory is onlined on the node, the node status changes
> > from A) to B).
> >
> > I feel this is very useful to manage "halfway status" of node
> > hotplug. (So, memory-less node patch is very helpful for me.)
> >
> > So, I would like to avoid using the word "node online" at here.
> > But, if above definition is messy for others, I'll change it.
>
> Ok can we talk about this as
>
> node online
>
> and
>
> node memory available?
Yes. Thanks.
--
Yasunori Goto
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