linux-kernel - Re: [PATCH -v2 0/9] mm: make movable onlining suck less

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Date:   Mon, 10 Apr 2017 18:02:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Igor Mammedov <imammedo@...hat.com>
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>,
        Jerome Glisse <jglisse@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
        slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Lai Jiangshan <laijs@...fujitsu.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Tobias Regnery <tobias.regnery@...il.com>
Subject: Re: [PATCH -v2 0/9] mm: make movable onlining suck less

On Mon 10-04-17 16:27:49, Igor Mammedov wrote:
[...]
> #issue3:
> removable flag flipped to non-removable state
> 
> // before series at commit ef0b577b6:
> memory32:offline removable: 0  zones: Normal Movable
> memory33:offline removable: 0  zones: Normal Movable
> memory34:offline removable: 0  zones: Normal Movable
> memory35:offline removable: 0  zones: Normal Movable

did you mean _after_ the series because the bellow looks like
the original behavior (at least valid_zones).
 
> // after series at commit 6a010434
> memory32:offline removable: 1  zones: Normal
> memory33:offline removable: 1  zones: Normal
> memory34:offline removable: 1  zones: Normal
> memory35:offline removable: 1  zones: Normal Movable
> 
> also looking at #issue1 removable flag state doesn't
> seem to be consistent between state changes but maybe that's
> been broken before

Well, the file has a very questionable semantic. It doesn't provide
a stable information. Anyway put that aside.
is_pageblock_removable_nolock relies on having zone association
which we do not have yet if the memblock is offline. So we need
the following. I will queue this as a preparatory patch.
---
>From 4f3ebc02f4d552d3fe114787ca8a38cc68702208 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Mon, 10 Apr 2017 17:59:03 +0200
Subject: [PATCH] mm, memory_hotplug: consider offline memblocks removable

is_pageblock_removable_nolock relies on having zone association to
examine all the page blocks to check whether they are movable or free.
This is just wasting of cycles when the memblock is offline. Later patch
in the series will also change the time when the page is associated with
a zone so we let's bail out early if the memblock is offline.

Reported-by: Igor Mammedov <imammedo@...hat.com>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 drivers/base/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 9677b6b711b0..0c29ec5598ea 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -128,6 +128,9 @@ static ssize_t show_mem_removable(struct device *dev,
 	int ret = 1;
 	struct memory_block *mem = to_memory_block(dev);
 
+	if (mem->stat != MEM_ONLINE)
+		goto out;
+
 	for (i = 0; i < sections_per_block; i++) {
 		if (!present_section_nr(mem->start_section_nr + i))
 			continue;
@@ -135,6 +138,7 @@ static ssize_t show_mem_removable(struct device *dev,
 		ret &= is_mem_section_removable(pfn, PAGES_PER_SECTION);
 	}
 
+out:
 	return sprintf(buf, "%d\n", ret);
 }
 
-- 
2.11.0


-- 
Michal Hocko
SUSE Labs