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

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Date:   Tue, 4 Apr 2017 10:59:10 -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 Tue, Apr 04, 2017 at 10:23:02AM +0200, Michal Hocko wrote:
>OK, so I've been thinkin about that and I believe that page_initialized
>check in get_nid_for_pfn is just bogus. There is nothing to rely on the
>page::lru to be already initialized. So I will go with the following as
>a separate preparatory patch.
>
>I believe the whole code should be revisited and I have put that on my
>ever growing todo list because I suspect that it is more complex than
>necessary. I suspect that memblock do not span more nodes and all this
>is just-in-case code (e.g. the onlining code assumes a single zone aka
>node. But let's do that later.
>
>---
>>From fd2e3b6eca1cf7766527203d23db6aca5957a3f1 Mon Sep 17 00:00:00 2001
>From: Michal Hocko <mhocko@...e.com>
>Date: Tue, 4 Apr 2017 10:05:06 +0200
>Subject: [PATCH] mm: drop page_initialized check from get_nid_for_pfn
>
>c04fc586c1a4 ("mm: show node to memory section relationship with
>symlinks in sysfs") has added means to export memblock<->node
>association into the sysfs. It has also introduced get_nid_for_pfn
>which is a rather confusing counterpart of pfn_to_nid which checks also
>whether the pfn page is already initialized (page_initialized).  This
>is done by checking page::lru != NULL which doesn't make any sense at
>all. Nothing in this path really relies on the lru list being used or
>initialized. Just remove it
>
>Signed-off-by: Michal Hocko <mhocko@...e.com>
>---
> drivers/base/node.c | 5 -----
> 1 file changed, 5 deletions(-)
>
>diff --git a/drivers/base/node.c b/drivers/base/node.c
>index 5548f9686016..ee080a35e869 100644
>--- a/drivers/base/node.c
>+++ b/drivers/base/node.c
>@@ -368,8 +368,6 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
>-#define page_initialized(page)  (page->lru.next)
>-
> static int __ref get_nid_for_pfn(unsigned long pfn)
> {
> 	struct page *page;
>@@ -380,9 +378,6 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
> 	if (system_state == SYSTEM_BOOTING)
> 		return early_pfn_to_nid(pfn);
> #endif
>-	page = pfn_to_page(pfn);
>-	if (!page_initialized(page))
>-		return -1;
> 	return pfn_to_nid(pfn);
> }
>

Verified that /sys/devices/system/node/nodeX/memoryY links are there now.

-- 
Reza Arbab