Re: [PATCH 2/6] mm: handle uninitialized numa nodes gracefully

Michal Hocko
2022-02-03T08:39:35Z

On Thu 03-02-22 09:23:20, Mike Rapoport wrote:
> On Thu, Feb 03, 2022 at 12:21:16AM +0000, Wei Yang wrote:
> > On Tue, Feb 01, 2022 at 10:54:37AM +0100, Michal Hocko wrote:
> > >On Tue 01-02-22 02:41:19, Wei Yang wrote:
> > >> On Thu, Jan 27, 2022 at 03:47:40PM +0100, Michal Hocko wrote:
> > >> [...]
> > >> >> > + /*
> > >> >> > + * not marking this node online because we do not want to
> > >> >> > + * confuse userspace by sysfs files/directories for node
> > >> >> > + * without any memory attached to it (see topology_init)
> > >> >> > + * The pgdat will get fully initialized when a memory is
> > >> >> > + * hotpluged into it by hotadd_init_pgdat
> > >> >> > + */
> > >>
> > >> Hmm... which following step would mark the node online? On x86, the node is
> > >> onlined in alloc_node_date(). This is not onlined here.
> > >
> > >The comment tries to explain that this happens during the memory
> > >hotplug. Or maybe I have missed your question?
> > >
> >
> > I am not sure for others, while the comment confused me a little.
> >
> > Currently in kernel, there are two situations for node online:
> >
> > * during memory hotplug
> > * during sys-init
> >
> > For memory hotplug, we allocate pgdat and online node. And current hot-add
> > process has already put them in two steps:
> >
> > 1. __try_online_node()
> > 2. node_set_online()
> >
> > So emphasize "not online" node here, confuse me a little. It is a natural
> > thing to not online node until it has memory.
> >
> > But from another point of view, the comment here is reasonable. During
> > sys-init, we online node at the same time when creating pgdat. And even for
> > memory-less node on x86, we online them too.
> >
> > Well, this is all about the comment. I have tried to grab may head but not
> > come up with a better idea.
> >
> > Or maybe this is just my personal feeling, don't bother if no-one else feel
> > like this.
>
> I shuffled the words a bit, maybe this sounds better not only to me :)
>
> /*
> * We do not want to confuse userspace by sysfs files/directories for node
> * without any memory attached to it, so this node is not marked as
> * N_MEMORY and not marked online so that topology_init() won't create
> * sysfs hierarchy for this node. The pgdat will get fully initialized by
> * hotadd_init_pgdat() when memory is hotpluged into this node
> */

Yes, I like this comment more than mine. Andrew could you replace it in
your tree or should I repost the patch?

Thanks!
--
Michal Hocko
SUSE Labs