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Date:   Tue, 7 May 2019 19:32:24 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Sasha Levin <sashal@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.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>
Subject: Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct
 pages for the full memory section
Message-ID: <20190507173224.GS31017@dhcp22.suse.cz>
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On Tue 07-05-19 13:18:06, Sasha Levin wrote:
> On Tue, May 07, 2019 at 10:15:19AM -0700, Linus Torvalds wrote:
> > On Tue, May 7, 2019 at 10:02 AM Sasha Levin <sashal@kernel.org> wrote:
> > > 
> > > I got it wrong then. I'll fix it up and get efad4e475c31 in instead.
> > 
> > Careful. That one had a bug too, and we have 891cb2a72d82 ("mm,
> > memory_hotplug: fix off-by-one in is_pageblock_removable").
> > 
> > All of these were *horribly* and subtly buggy, and might be
> > intertwined with other issues. And only trigger on a few specific
> > machines where the memory map layout is just right to trigger some
> > special case or other, and you have just the right config.
> > 
> > It might be best to verify with Michal Hocko. Michal?
> 
> 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.
-- 
Michal Hocko
SUSE Labs