From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-pl1-f198.google.com (mail-pl1-f198.google.com [209.85.214.198])
	by kanga.kvack.org (Postfix) with ESMTP id 2083D6B7901
	for <linux-mm@kvack.org>; Thu,  6 Dec 2018 03:32:11 -0500 (EST)
Received: by mail-pl1-f198.google.com with SMTP id ay11so16773646plb.20
        for <linux-mm@kvack.org>; Thu, 06 Dec 2018 00:32:11 -0800 (PST)
Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15])
        by mx.google.com with ESMTPS id x128si23282432pfb.128.2018.12.06.00.32.09
        for <linux-mm@kvack.org>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Thu, 06 Dec 2018 00:32:10 -0800 (PST)
Date: Thu, 6 Dec 2018 09:32:06 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [RFC PATCH] hwpoison, memory_hotplug: allow hwpoisoned pages to
 be offlined
Message-ID: <20181206083206.GC1286@dhcp22.suse.cz>
References: <20181203100309.14784-1-mhocko@kernel.org>
 <20181205122918.GL1286@dhcp22.suse.cz>
 <20181205165716.GS1286@dhcp22.suse.cz>
 <20181206052137.GA28595@hori1.linux.bs1.fc.nec.co.jp>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20181206052137.GA28595@hori1.linux.bs1.fc.nec.co.jp>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Oscar Salvador <OSalvador@suse.com>, Andrew Morton <akpm@linux-foundation.org>, Dan Williams <dan.j.williams@gmail.com>, Pavel Tatashin <pasha.tatashin@soleen.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Stable tree <stable@vger.kernel.org>

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@ah.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