linux-kernel - Re: [-next] memory hotplug regression

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Date:   Wed, 31 May 2017 08:24:40 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Gerald Schaefer <gerald.schaefer@...ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [-next] memory hotplug regression

On Tue 30-05-17 16:55:01, Heiko Carstens wrote:
> On Tue, May 30, 2017 at 04:32:47PM +0200, Michal Hocko wrote:
> > On Tue 30-05-17 14:37:24, Heiko Carstens wrote:
> > > On Tue, May 30, 2017 at 02:18:06PM +0200, Michal Hocko wrote:
> > > > > So ZONE_DMA ends within ZONE_NORMAL. This shouldn't be possible, unless
> > > > > this restriction is gone?
> > > > 
> > > > The patch below should help.
> > > 
> > > It does fix this specific problem, but introduces a new one:
> > > 
> > > # echo online_movable > /sys/devices/system/memory/memory16/state
> > > # cat /sys/devices/system/memory/memory16/valid_zones
> > > Movable
> > > # echo offline > /sys/devices/system/memory/memory16/state
> > > # cat /sys/devices/system/memory/memory16/valid_zones
> > >           <--- no output
> > > 
> > > Memory block 16 is the only one I onlined and offlineto ZONE_MOVABLE.
> > 
> > Could you test the this on top please?
> > ---
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 792c098e0e5f..a26f9f8e6365 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -937,13 +937,18 @@ void __ref move_pfn_range_to_zone(struct zone *zone,
> >  	set_zone_contiguous(zone);
> >  }
> > 
> > +/*
> > + * Returns a default kernel memory zone for the given pfn range.
> > + * If no kernel zone covers this pfn range it will automatically go
> > + * to the ZONE_NORMAL.
> > + */
> >  struct zone *default_zone_for_pfn(int nid, unsigned long start_pfn,
> >  		unsigned long nr_pages)
> >  {
> >  	struct pglist_data *pgdat = NODE_DATA(nid);
> >  	int zid;
> > 
> > -	for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> > +	for (zid = 0; zid <= ZONE_NORMAL; zid++) {
> >  		struct zone *zone = &pgdat->node_zones[zid];
> > 
> >  		if (zone_intersects(zone, start_pfn, nr_pages))
> 
> Still broken, but in different way(s):
> 
> # cat /sys/devices/system/memory/memory16/valid_zones
> Normal Movable
> # echo online_movable > /sys/devices/system/memory/memory16/state
> # cat /sys/devices/system/memory/memory16/valid_zones
> Movable
> # cat /sys/devices/system/memory/memory18/valid_zones
> Movable
> # echo online > /sys/devices/system/memory/memory18/state
> # cat /sys/devices/system/memory/memory18/valid_zones
> Normal    <--- should be Movable
> # cat /sys/devices/system/memory/memory17/valid_zones
>           <--- no output

OK, so this is an independent problem and an unrelated one to the
patch I've posted. We need two patches actually. Damn, I hate
MMOP_ONLINE_KEEP. I will send 2 patches as a reply to this email.

-- 
Michal Hocko
SUSE Labs