linux-kernel - Re: [RFC PATCH] x86, numa: always initialize all possible nodes

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Message-ID: <20190211145217.GE15609@dhcp22.suse.cz>
Date:   Mon, 11 Feb 2019 15:52:17 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        Pingfan Liu <kernelfans@...il.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Tony Luck <tony.luck@...el.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-ia64@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86, numa: always initialize all possible nodes

On Mon 11-02-19 14:49:09, Ingo Molnar wrote:
> 
> * Michal Hocko <mhocko@...nel.org> wrote:
> 
> > On Thu 24-01-19 11:10:50, Dave Hansen wrote:
> > > On 1/24/19 6:17 AM, Michal Hocko wrote:
> > > > and nr_cpus set to 4. The underlying reason is tha the device is bound
> > > > to node 2 which doesn't have any memory and init_cpu_to_node only
> > > > initializes memory-less nodes for possible cpus which nr_cpus restrics.
> > > > This in turn means that proper zonelists are not allocated and the page
> > > > allocator blows up.
> > > 
> > > This looks OK to me.
> > > 
> > > Could we add a few DEBUG_VM checks that *look* for these invalid
> > > zonelists?  Or, would our existing list debugging have caught this?
> > 
> > Currently we simply blow up because those zonelists are NULL. I do not
> > think we have a way to check whether an existing zonelist is actually 
> > _correct_ other thatn check it for NULL. But what would we do in the
> > later case?
> > 
> > > Basically, is this bug also a sign that we need better debugging around
> > > this?
> > 
> > My earlier patch had a debugging printk to display the zonelists and
> > that might be worthwhile I guess. Basically something like this
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 2e097f336126..c30d59f803fb 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5259,6 +5259,11 @@ static void build_zonelists(pg_data_t *pgdat)
> >  
> >  	build_zonelists_in_node_order(pgdat, node_order, nr_nodes);
> >  	build_thisnode_zonelists(pgdat);
> > +
> > +	pr_info("node[%d] zonelist: ", pgdat->node_id);
> > +	for_each_zone_zonelist(zone, z, &pgdat->node_zonelists[ZONELIST_FALLBACK], MAX_NR_ZONES-1)
> > +		pr_cont("%d:%s ", zone_to_nid(zone), zone->name);
> > +	pr_cont("\n");
> >  }
> 
> Looks like this patch fell through the cracks - any update on this?

I was waiting for some feedback. As there were no complains about the
above debugging output I will make it a separate patch and post both
patches later this week. I just have to go through my backlog pile after
vacation.
-- 
Michal Hocko
SUSE Labs