linux-kernel - Re: [RFC PATCH] hwpoison, memory_hotplug: allow hwpoisoned pages to be offlined

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Date:   Thu, 6 Dec 2018 05:21:38 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Oscar Salvador <OSalvador@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...il.com>,
        "Pavel Tatashin" <pasha.tatashin@...een.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stable tree <stable@...r.kernel.org>
Subject: Re: [RFC PATCH] hwpoison, memory_hotplug: allow hwpoisoned pages to
 be offlined

On Wed, Dec 05, 2018 at 05:57:16PM +0100, Michal Hocko wrote:
> On Wed 05-12-18 13:29:18, Michal Hocko wrote:
> [...]
> > After some more thinking I am not really sure the above reasoning is
> > still true with the current upstream kernel. Maybe I just managed to
> > confuse myself so please hold off on this patch for now. Testing by
> > Oscar has shown this patch is helping but the changelog might need to be
> > updated.
> 
> OK, so Oscar has nailed it down and it seems that 4.4 kernel we have
> been debugging on behaves slightly different. The underlying problem is
> the same though. So I have reworded the changelog and added "just in
> case" PageLRU handling. Naoya, maybe you have an argument that would
> make this void for current upstream kernels.

The following commit (not in 4.4.x stable tree) might explain the
difference you experienced:

  commit 286c469a988fbaf68e3a97ddf1e6c245c1446968                          
  Author: Naoya Horiguchi <n-horiguchi@...jp.nec.com>                      
  Date:   Wed May 3 14:56:22 2017 -0700                                    
                                                                           
      mm: hwpoison: call shake_page() after try_to_unmap() for mlocked page

This commit adds shake_page() for mlocked pages to make sure that the target
page is flushed out from LRU cache. Without this shake_page(), subsequent
delete_from_lru_cache() (from me_pagecache_clean()) fails to isolate it and
the page will finally return back to LRU list.  So this scenario leads to
"hwpoisoned by still linked to LRU list" page.

Thanks,
Naoya Horiguchi