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

[Naoya Horiguchi]

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@xxxxxxxxxxxxx>                      
  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