linux-kernel - Re: [PATCH 1/2] mm, memory_hotplug: fix MMOP_ONLINE

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Date:   Thu, 1 Jun 2017 14:40:22 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Mel Gorman <mgorman@...e.de>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
        slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm, memory_hotplug: fix MMOP_ONLINE_KEEP behavior

On Thu 01-06-17 14:32:42, Vlastimil Babka wrote:
> On 06/01/2017 10:37 AM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > Heiko Carstens has noticed that the MMOP_ONLINE_KEEP is broken currently
> > $ grep . memory3?/valid_zones
> > memory34/valid_zones:Normal Movable
> > memory35/valid_zones:Normal Movable
> > memory36/valid_zones:Normal Movable
> > memory37/valid_zones:Normal Movable
> > 
> > $ echo online_movable > memory34/state
> > $ grep . memory3?/valid_zones
> > memory34/valid_zones:Movable
> > memory35/valid_zones:Movable
> > memory36/valid_zones:Movable
> > memory37/valid_zones:Movable
> > 
> > $ echo online > memory36/state
> > $ grep . memory3?/valid_zones
> > memory34/valid_zones:Movable
> > memory36/valid_zones:Normal
> > memory37/valid_zones:Movable
> > 
> > so we have effectivelly punched a hole into the movable zone. The
> > problem is that move_pfn_range() check for MMOP_ONLINE_KEEP is wrong.
> > It only checks whether the given range is already part of the movable
> > zone which is not the case here as only memory34 is in the zone. Fix
> > this by using allow_online_pfn_range(..., MMOP_ONLINE_KERNEL) if that
> > is false then we can be sure that movable onlining is the right thing to
> > do.
> > 
> > Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
> > Tested-by: Heiko Carstens <heiko.carstens@...ibm.com>
> > Fixes: "mm, memory_hotplug: do not associate hotadded memory to zones until online"
> 
> Just fold it there before sending to Linus, right?

I do not have a strong preference. The changelog could still be helpful
for reference. The original patch is quite large and details like this
are likely to get lost there.

> 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!
-- 
Michal Hocko
SUSE Labs