linux-kernel - Re: [PATCH v6 00/12] HWPOISON: soft offline rework

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Message-ID: <20200811035612.GA6143@hori.linux.bs1.fc.nec.co.jp>
Date:   Tue, 11 Aug 2020 03:56:13 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Qian Cai <cai@....pw>
CC:     "nao.horiguchi@...il.com" <nao.horiguchi@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>,
        "zeil@...dex-team.ru" <zeil@...dex-team.ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        <linux-arm-kernel@...ts.infradead.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>
Subject: Re: [PATCH v6 00/12] HWPOISON: soft offline rework

On Mon, Aug 10, 2020 at 11:45:36PM -0400, Qian Cai wrote:
> 
> 
> > On Aug 10, 2020, at 11:11 PM, HORIGUCHI NAOYA(堀口　直也) <naoya.horiguchi@....com> wrote:
> > 
> > I'm still not sure why the test succeeded by reverting these because
> > current mainline kernel provides similar mechanism to prevent reuse of
> > soft offlined page. So this success seems to me something suspicious.
> 
> Even if we call munmap() on the range, it still can’t be be reused? If so, how to recover those memory then?

No, it can't, because soft offline isolates the physical page.
so even after calling munmap(), the side effect remains on the page.
In your random.c, memory online/offline resets the status of hwpoison.
So you can reallocate hugepages in another run of the program.

> 
> > 
> > To investigate more, I want to have additional info about the page states
> > of the relevant pages after soft offlining.  Could you collect it by the
> > following steps?
> 
> Do you want to collect those from the failed or succeed kernel?

I'd like to check on the succeeded kernel.
Sorry for the lack of information.

Thanks,
Naoya Horiguchi