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

Mike Rapoport
2022-02-03T07:23:34Z

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
*/

--
Sincerely yours,
Mike.