linux-kernel - Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct pages for the full memory section

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Message-ID: <20190507174514.GI1747@sasha-vm>
Date:   Tue, 7 May 2019 13:45:14 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Mikhail Zaslonko <zaslonko@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...rosoft.com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct
 pages for the full memory section

On Tue, May 07, 2019 at 10:36:55AM -0700, Matthew Wilcox wrote:
>On Tue, May 07, 2019 at 07:32:24PM +0200, Michal Hocko wrote:
>> On Tue 07-05-19 13:18:06, Sasha Levin wrote:
>> > Michal, is there a testcase I can plug into kselftests to make sure we
>> > got this right (and don't regress)? We care a lot about memory hotplug
>> > working right.
>>
>> As said in other email. The memory hotplug tends to work usually. It
>> takes unexpected memory layouts which trigger corner cases. This makes
>> testing really hard.
>
>Can we do something with qemu?  Is it flexible enough to hotplug memory
>at the right boundaries?

That was my thinking too. qemu should be able to reproduce all these
"unexpected" memory layouts we've had issue with so far and at the very
least make sure we don't regress on those.

We're going to have (quite a) large amount of systems with "weird"
memory layouts that do memory hotplug quite frequently in production, so
this whole "tends to work usually" thing kinda scares me.

--
Thanks,
Sasha