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Date: Wed, 24 May 2017 15:50:21 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Igor Mammedov <imammedo@redhat.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
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        Daniel Kiper <daniel.kiper@oracle.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 2/2] mm, memory_hotplug: drop CONFIG_MOVABLE_NODE
Message-ID: <20170524135020.GI14733@dhcp22.suse.cz>
References: <20170524122411.25212-1-mhocko@kernel.org>
 <20170524122411.25212-3-mhocko@kernel.org>
 <20170524153017.7a66368d@nial.brq.redhat.com>
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On Wed 24-05-17 15:30:17, Igor Mammedov wrote:
> On Wed, 24 May 2017 14:24:11 +0200
> Michal Hocko <mhocko@kernel.org> wrote:
> 
> [...]
> > index facc20a3f962..ec7d6ae01c96 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2246,8 +2246,11 @@
> [...]
> > +			movable. This means that the memory of such nodes
> > +			will be usable only for movable allocations which
> > +			rules out almost all kernel allocations. Use with
> > +			caution!
> maybe dumb question but, is it really true that kernel won't ever
> do kernel allocations from movable zone?
> 
> looking at kmalloc(slab): we can get here:
> 
> get_page_from_freelist() ->
>     rmqueue() ->
>         __rmqueue() ->
>             __rmqueue_fallback() ->
>                 find_suitable_fallback()
> 
> and it might return movable fallback and page could be stolen from there.

No, you are mixing movable/unmovable pageblocks and movable zones.
Movable zone basically works the same way as the Highmem zone. Have a
look at gfp_zone() and high_zoneidx usage in get_page_from_freelist
-- 
Michal Hocko
SUSE Labs