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

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Date:   Thu, 6 Dec 2018 09:32:06 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
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 Thu 06-12-18 05:21:38, Naoya Horiguchi wrote:
> 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.

OK, I see. So does that mean that the LRU handling is no longer needed
and there is a guanratee that all kernels with the above commit cannot
ever get an LRU page?
-- 
Michal Hocko
SUSE Labs