Re: [PATCH v2 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline

Srikar Dronamraju
2020-04-29T01:42:11Z

> >
> > By marking, N_ONLINE as NODE_MASK_NONE, lets stop assuming that Node 0 is
> > always online.
> >
> > ...
> >
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -116,8 +116,10 @@ EXPORT_SYMBOL(latent_entropy);
> > */
> > nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
> > [N_POSSIBLE] = NODE_MASK_ALL,
> > +#ifdef CONFIG_NUMA
> > + [N_ONLINE] = NODE_MASK_NONE,
> > +#else
> > [N_ONLINE] = { { [0] = 1UL } },
> > -#ifndef CONFIG_NUMA
> > [N_NORMAL_MEMORY] = { { [0] = 1UL } },
> > #ifdef CONFIG_HIGHMEM
> > [N_HIGH_MEMORY] = { { [0] = 1UL } },
>
> So on all other NUMA machines, when does node 0 get marked online?
>
> This change means that for some time during boot, such machines will
> now be running with node 0 marked as offline. What are the
> implications of this? Will something break?

Till the nodes are detected, marking Node 0 as online tends to be redundant.
Because the system doesn't know if its a NUMA or a non-NUMA system.
Once we detect the nodes, we online them immediately. Hence I don't see any
side-effects or negative implications of this change.

However if I am missing anything, please do let me know.

From my part, I have tested this on
1. Non-NUMA Single node but CPUs and memory coming from zero node.
2. Non-NUMA Single node but CPUs and memory coming from non-zero node.
3. NUMA Multi node but with CPUs and memory from node 0.
4. NUMA Multi node but with no CPUs and memory from node 0.

--
Thanks and Regards
Srikar Dronamraju