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

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Date:   Mon, 3 Apr 2017 15:42:13 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, 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 Mon, Apr 03, 2017 at 10:23:38PM +0200, Michal Hocko wrote:
>On Mon 03-04-17 14:58:30, Reza Arbab wrote:
>> However, I am seeing a regression. When adding memory to a memoryless 
>> node, it shows up in node 0 instead. I'm digging to see if I can help 
>> narrow down where things go wrong.
>
>OK, I guess I know what is going on here. online_pages relies on
>pfn_to_nid(pfn) to return a proper node. But we are doing
>page_to_nid(pfn_to_page(__pfn_to_nid_pfn)) so we rely on the page being
>properly initialized. Damn, I should have noticed that. There are two
>ways around that. Either the __add_section stores the nid into the
>struct page and make page_to_nid reliable or store it somewhere else
>(ideally into the memblock). The first is easier (let's do it for now)
>but longterm we do not want to rely on the struct page at all I believe.
>
>Does the following help?
>---
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index b9dc1c4e26c3..0e21b9f67c9d 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -309,14 +309,19 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn)
>
> 	/*
> 	 * Make all the pages reserved so that nobody will stumble over half
>-	 * initialized state.
>+	 * initialized state.
>+	 * FIXME: We also have to associate it with a node because pfn_to_node
>+	 * relies on having page with the proper node.
> 	 */
> 	for (i = 0; i < PAGES_PER_SECTION; i++) {
> 		unsigned long pfn = phys_start_pfn + i;
>+		struct page *page;
> 		if (!pfn_valid(pfn))
> 			continue;
>
>-		SetPageReserved(pfn_to_page(phys_start_pfn + i));
>+		page = pfn_to_page(pfn);
>+		set_page_node(page, nid);
>+		SetPageReserved(page);
> 	}
>
> 	return register_new_memory(nid, __pfn_to_section(phys_start_pfn));

Almost there. I'm seeing the memory in the correct node now, but the 
/sys/devices/system/node/nodeX/memoryY links are not being created.

I think it's tripping up here, in register_mem_sect_under_node():

		page_nid = get_nid_for_pfn(pfn);
		if (page_nid < 0)
			continue;

-- 
Reza Arbab