linux-kernel - Re: [PATCH] mm: take memory hotplug lock within numa_zonelist_order

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Date:   Wed, 26 Jul 2017 14:19:52 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andre Wild <wild@...ux.vnet.ibm.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: take memory hotplug lock within
 numa_zonelist_order_handler()

On Wed 26-07-17 13:48:12, Heiko Carstens wrote:
> On Wed, Jul 26, 2017 at 01:31:12PM +0200, Michal Hocko wrote:
> > On Wed 26-07-17 13:17:38, Heiko Carstens wrote:
> > [...]
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 6d30e914afb6..fc32aa81f359 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -4891,9 +4891,11 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
> > >  				NUMA_ZONELIST_ORDER_LEN);
> > >  			user_zonelist_order = oldval;
> > >  		} else if (oldval != user_zonelist_order) {
> > > +			mem_hotplug_begin();
> > >  			mutex_lock(&zonelists_mutex);
> > >  			build_all_zonelists(NULL, NULL);
> > >  			mutex_unlock(&zonelists_mutex);
> > > +			mem_hotplug_done();
> > >  		}
> > >  	}
> > >  out:
> > 
> > Please note that this code has been removed by
> > http://lkml.kernel.org/r/20170721143915.14161-2-mhocko@kernel.org. It
> > will get to linux-next as soon as Andrew releases a new version mmotm
> > tree.
> 
> We still would need something for 4.13, no?

If this presents a real problem then yes. Has this happened in a real
workload or during some artificial test? I mean the code has been like
that for ages and nobody noticed/reported any problems.

That being said, I do not have anything against your patch. It is
trivial to rebase mine on top of yours. I am just not sure it is worth
the code churn. E.g. do you think this patch is a stable backport
material?
-- 
Michal Hocko
SUSE Labs