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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 7 May 2019 10:43:31 -0700
Message-ID: <CAHk-=wjFkwKpRGP-MJA6mM6ZOu0aiqtvmqxKR78HHXVd_SwpUg@mail.gmail.com>
Subject: Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct
 pages for the full memory section
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Michal Hocko <mhocko@kernel.org>, Sasha Levin <sashal@kernel.org>,
        Alexander Duyck <alexander.duyck@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        Mikhail Zaslonko <zaslonko@linux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>,
        Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Pasha Tatashin <Pavel.Tatashin@microsoft.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sasha Levin <alexander.levin@microsoft.com>,
        linux-mm <linux-mm@kvack.org>
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On Tue, May 7, 2019 at 10:36 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> Can we do something with qemu?  Is it flexible enough to hotplug memory
> at the right boundaries?

It's not just the actual hotplugged memory, it's things like how the
e820 tables were laid out for the _regular_ non-hotplug stuff too,
iirc to get the cases where something didn't work out.

I'm sure it *could* be emulated, and I'm sure some hotplug (and page
poison errors etc) testing in qemu would be lovely and presumably some
people do it, but all the cases so far have been about odd small
special cases that people didn't think of and didn't hit. I'm not sure
the qemu testing would think of them either..

                Linus