linux-kernel - Re: [PATCH 2/6] mm/memblock: make full utilization of numa info

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Date:   Tue, 26 Feb 2019 13:40:05 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Jonathan Corbet <corbet@....net>,
        Nicholas Piggin <npiggin@...il.com>,
        Daniel Vacek <neelx@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] mm/memblock: make full utilization of numa info

On Mon, Feb 25, 2019 at 11:34 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 2/24/19 4:34 AM, Pingfan Liu wrote:
> > +/*
> > + * build_node_order() relies on cpumask_of_node(), hence arch should
> > + * set up cpumask before calling this func.
> > + */
>
> Whenever I see comments like this, I wonder what happens if the arch
> doesn't do this?  Do we just crash in early boot in wonderful new ways?
>  Or do we get a nice message telling us?
>
If doesn't do this, this function will crash. It is a shame but a
little hard to work around, since this function is called at early
boot stage, things like cpumask_of_node(cpu_to_node(cpu)) can not work
reliably, and we lack of an abstract interface to get such information
from all archs. So I leave this to arch's developer.

> > +void __init memblock_build_node_order(void)
> > +{
> > +     int nid, i;
> > +     nodemask_t used_mask;
> > +
> > +     node_fallback = memblock_alloc(MAX_NUMNODES * sizeof(int *),
> > +             sizeof(int *));
> > +     for_each_online_node(nid) {
> > +             node_fallback[nid] = memblock_alloc(
> > +                     num_online_nodes() * sizeof(int), sizeof(int));
> > +             for (i = 0; i < num_online_nodes(); i++)
> > +                     node_fallback[nid][i] = NUMA_NO_NODE;
> > +     }
> > +
> > +     for_each_online_node(nid) {
> > +             nodes_clear(used_mask);
> > +             node_set(nid, used_mask);
> > +             build_node_order(node_fallback[nid], num_online_nodes(),
> > +                     nid, &used_mask);
> > +     }
> > +}
>
> This doesn't get used until patch 6 as far as I can tell.  Was there a
> reason to define it here?
>
Yes, it gets used until patch 6. Patch 6 has two groups of
pre-requirements [1-2] and [3-5]. Do you think reorder the patches and
moving [3-5] ahead of [1-2] is a better choice?

Thanks and regards,
Pingfan