linux-kernel - Re: [PATCH 0/6] mm: make movable onlining suck less

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Date:   Thu, 6 Apr 2017 18:21:55 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>, Mel Gorman <mgorman@...e.de>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Tang Chen <tangchen@...fujitsu.com>, qiuxishi@...wei.com,
        Kani Toshimitsu <toshi.kani@....com>, slaoub@...il.com,
        Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Zhang Zhen <zhenzhang.zhang@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dan Williams <dan.j.williams@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Lai Jiangshan <laijs@...fujitsu.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 0/6] mm: make movable onlining suck less

On Thu 06-04-17 10:46:53, Reza Arbab wrote:
> On Thu, Apr 06, 2017 at 05:41:28PM +0200, Michal Hocko wrote:
> >On Thu 06-04-17 10:24:49, Reza Arbab wrote:
> >>On Thu, Apr 06, 2017 at 03:08:46PM +0200, Michal Hocko wrote:
> >>>OK, so after recent change mostly driven by testing from Reza Arbab
> >>>(thanks again) I believe I am getting to a working state finally. All I
> >>>currently have is
> >>>in git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git tree
> >>>attempts/rewrite-mem_hotplug-WIP branch. I will highly appreciate more
> >>>testing of course and if there are no new issues found I will repost the
> >>>series for the review.
> >>
> >>Looking good! I can do my add/remove/repeat test and things seem fine.
> >>
> >>One thing--starting on the second iteration, I am seeing the WARN in
> >>free_area_init_node();
> >>
> >>add_memory
> >> add_memory_resource
> >>   hotadd_new_pgdat
> >>     free_area_init_node
> >>	WARN_ON(pgdat->nr_zones || pgdat->kswapd_classzone_idx);
> >
> >Have you tested with my attempts/rewrite-mem_hotplug-WIP mentioned
> >elsewhere? Because I suspect that "mm: get rid of zone_is_initialized"
> >might cause this.
> 
> This was my first time using your git branch instead of applying the patches
> from this thread to v4.11-rc5 myself.

OK, so this looks like another thing to resolve. I have seen this
warning as well but I didn't consider it relevant because I had to tweak
the code make the node go offline (removed check_and_unmap_cpu_on_node
from try_offline_node) so I thought it was a fallout from there. 

But let's have a look. hotadd_new_pgdat does for an existing pgdat
		/* Reset the nr_zones, order and classzone_idx before reuse */
		pgdat->nr_zones = 0;
		pgdat->kswapd_order = 0;
		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;

so free_area_init_node absolutely has to hit this warning. This is not
in the Linus tree because it is still in Andrew's mmotm coming from
http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-vmscan-prevent-kswapd-sleeping-prematurely-due-to-mismatched-classzone_idx.patch

So yay, finally that doesn't come from me. Mel, I guess that either
hotadd_new_pgdat should keep its kswapd_classzone_idx = 0 or the warning
should be updated.

-- 
Michal Hocko
SUSE Labs