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

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Message-Id: <20170405173248.4vtdgk2kolbzztya@arbab-laptop>
Date:   Wed, 5 Apr 2017 12:32:49 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mel Gorman <mgorman@...e.de>, 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 Wed, Apr 05, 2017 at 05:42:59PM +0200, Michal Hocko wrote:
>But one thing that is really bugging me is how could you see low pfns 
>in the previous oops. Please drop the last patch and sprinkle printks 
>down the remove_memory path to see where this all go south. I believe 
>that there is something in the initialization code lurking in my code. 
>Please also scratch the pfn_valid check in online_pages diff. It will 
>not help here.

Got it. 

shrink_pgdat_span: start_pfn=0x10000, end_pfn=0x10100, pgdat_start_pfn=0x0, pgdat_end_pfn=0x20000

The problem is that pgdat_start_pfn here should be 0x10000. As you 
suspected, it never got set. This fixes things for me.

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 623507f..37c1b63 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -884,7 +884,7 @@ static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned lon
 {
 	unsigned long old_end_pfn = pgdat_end_pfn(pgdat);
 
-	if (start_pfn < pgdat->node_start_pfn)
+	if (!pgdat->node_spanned_pages || start_pfn < pgdat->node_start_pfn)
 		pgdat->node_start_pfn = start_pfn;
 
 	pgdat->node_spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - pgdat->node_start_pfn;
---

Along these lines, maybe we should also do

-	if (start_pfn < zone->zone_start_pfn)
+	if (zone_is_empty(zone) || start_pfn < zone->zone_start_pfn)

in resize_zone_range()?

-- 
Reza Arbab