linux-kernel - [PATCH] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove

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Message-Id: <1568612857-10395-1-git-send-email-anshuman.khandual@arm.com>
Date:   Mon, 16 Sep 2019 11:17:37 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove_memory()

In add_memory_resource() the memory range to be hot added first gets into
the memblock via memblock_add() before arch_add_memory() is called on it.
Reverse sequence should be followed during memory hot removal which already
is being followed in add_memory_resource() error path. This now ensures
required re-order between memblock_[free|remove]() and arch_remove_memory()
during memory hot-remove.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Michal Hocko <mhocko@...e.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Pavel Tatashin <pasha.tatashin@...een.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
Original patch https://lkml.org/lkml/2019/9/3/327

Memory hot remove now works on arm64 without this because a recent commit
60bb462fc7ad ("drivers/base/node.c: simplify unregister_memory_block_under_nodes()").

David mentioned that re-ordering should still make sense for consistency
purpose (removing stuff in the reverse order they were added). This patch
is now detached from arm64 hot-remove series.

https://lkml.org/lkml/2019/9/3/326

 mm/memory_hotplug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c73f09913165..355c466e0621 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
 
 	/* remove memmap entry */
 	firmware_map_remove(start, start + size, "System RAM");
-	memblock_free(start, size);
-	memblock_remove(start, size);
 
 	/* remove memory block devices before removing memory */
 	remove_memory_block_devices(start, size);
 
 	arch_remove_memory(nid, start, size, NULL);
+	memblock_free(start, size);
+	memblock_remove(start, size);
 	__release_memory_resource(start, size);
 
 	try_offline_node(nid);
-- 
2.20.1