Re: [PATCH] arm64: NUMA: Kconfig: Increase max number of nodes

[Vanshi Konda]

On Tue, Oct 20, 2020 at 07:09:36PM +0100, Valentin Schneider wrote:
> Hi,
>
> Nit on the subject: this only increases the default, the max is still 2?????.
>
> On 20/10/20 18:34, Vanshidhar Konda wrote:
> > The current arm64 max NUMA nodes default to 4. Today's arm64 systems can
> > reach or exceed 16. Increase the number to 64 (matching x86_64).
> >
> > Signed-off-by: Vanshidhar Konda <vanshikonda@xxxxxxxxxxxxxxxxxxxxxx>
> > ---
> >  arch/arm64/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 893130ce1626..3e69d3c981be 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -980,7 +980,7 @@ config NUMA
> >  config NODES_SHIFT
> >       int "Maximum NUMA Nodes (as a power of 2)"
> >       range 1 10
> > -	default "2"
> > +	default "6"
>
> This leads to more statically allocated memory for things like node to CPU
> maps (see uses of MAX_NUMNODES), but that shouldn't be too much of an
> issue.
>
> AIUI this also directly correlates to how many more page->flags bits are
> required: are we sure the max 10 works on any aarch64 platform? I'm

I created an experimental setup in which I enabled 1024 NUMA nodes in 
SRAT, SLIT and configured NODES_SHIFT=10 for the kernel. 1022 of these 
nodes were memory-only NUMA nodes. This configuration booted and 
recognized the NUMA nodes correctly.

> genuinely asking here, given that I'm mostly a stranger to the mm
> world. The default should be something we're somewhat confident works
> everywhere.
>
> >       depends on NEED_MULTIPLE_NODES
> >       help
> >         Specify the maximum number of NUMA Nodes available on the target