linux-kernel - Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

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Message-ID: <20191022091431.GG9379@dhcp22.suse.cz>
Date:   Tue, 22 Oct 2019 11:14:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Pingfan Liu <kernelfans@...il.com>, Qian Cai <cai@....pw>,
        Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

On Tue 22-10-19 10:32:11, David Hildenbrand wrote:
[...]
> E.g., arch/x86/kvm/mmu.c:kvm_is_mmio_pfn()

Thanks for these references. I am not really familiar with kvm so I
cannot really comment on the specific code but I am wondering why
it simply doesn't check for ZONE_DEVICE explicitly? Also we do care
about holes in RAM (from the early boot), those should be reserved
already AFAIR. So we are left with hotplugged memory with holes and
I am not really sure we should bother with this until there is a clear
usecase in sight.
-- 
Michal Hocko
SUSE Labs