linux-kernel - Re: [PATCH v3] x86/numa_emulation: Fix uniform-split numa emulation

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Date:   Thu, 25 Oct 2018 13:55:53 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        stable <stable@...r.kernel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        alexander.h.duyck@...ux.intel.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86/numa_emulation: Fix uniform-split numa emulation

On Thu, Oct 25, 2018 at 1:52 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 10/25/18 1:26 PM, Dan Williams wrote:
> > --- a/arch/x86/mm/numa_emulation.c
> > +++ b/arch/x86/mm/numa_emulation.c
> > @@ -400,9 +400,17 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
> >               n = simple_strtoul(emu_cmdline, &emu_cmdline, 0);
> >               ret = -1;
> >               for_each_node_mask(i, physnode_mask) {
> > +                     /*
> > +                      * The reason we pass in blk[0] is due to
> > +                      * numa_remove_memblk_from() called by
> > +                      * emu_setup_memblk() will delete entry 0
> > +                      * and then move everything else up in the pi.blk
> > +                      * array. Therefore we should always be looking
> > +                      * at blk[0].
> > +                      */
> >                       ret = split_nodes_size_interleave_uniform(&ei, &pi,
> > -                                     pi.blk[i].start, pi.blk[i].end, 0,
> > -                                     n, &pi.blk[i], nid);
> > +                                     pi.blk[0].start, pi.blk[0].end, 0,
> > +                                     n, &pi.blk[0], nid);
>
> So, has this *ever* worked on a multi-socket configuration?  Or has it
> just never been run on a multi-socket configuration?

It happened to work on 2-socket. We only saw issues when moving to
4-socket and above, and sometimes only a grey failure with an
odd-sized node not outright crash / boot failure.

> Either way, nice changelog, and nice comments.  I'd have some minor nits
> if you have to respin it, but otherwise:
>
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>

Thanks.