linux-kernel - Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from hotadded memory

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Message-ID: <20170728120141.GK2274@dhcp22.suse.cz>
Date:   Fri, 28 Jul 2017 14:01:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        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>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from
 hotadded memory

On Wed 26-07-17 10:33:28, Michal Hocko wrote:
[...]
> There is also one potential drawback, though. If somebody uses memory
> hotplug for 1G (gigantic) hugetlb pages then this scheme will not work
> for them obviously because each memory section will contain 2MB reserved
> area.

Actually I am wrong here. It is not each section in general. I have
completely forgot that we do large memblocks on x86_64 with a lot of
memory and then we hotadd 2GB memblocks and the altmap will allocate
from the beginign of the _memblock_ and so all the memmaps will end up
in the first memory section.
-- 
Michal Hocko
SUSE Labs