linux-kernel - [RESEND PATCH] mm/hotplug: don't reset pagetype flags for offline

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Message-Id: <20190310200102.88014-1-cai@lca.pw>
Date:   Sun, 10 Mar 2019 16:01:02 -0400
From:   Qian Cai <cai@....pw>
To:     akpm@...ux-foundation.org
Cc:     mhocko@...e.com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qian Cai <cai@....pw>
Subject: [RESEND PATCH] mm/hotplug: don't reset pagetype flags for offline

The commit f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
memory to zones until online") introduced move_pfn_range_to_zone() which
calls memmap_init_zone() during onlining a memory block.
memmap_init_zone() will reset pagetype flags and makes migrate type to
be MOVABLE.

However, in __offline_pages(), it also call undo_isolate_page_range()
after offline_isolated_pages() to do the same thing. Due to
the commit 2ce13640b3f4 ("mm: __first_valid_page skip over offline
pages") changed __first_valid_page() to skip offline pages,
undo_isolate_page_range() here just waste CPU cycles looping around the
offlining PFN range while doing nothing, because __first_valid_page()
will return NULL as offline_isolated_pages() has already marked all
memory sections within the pfn range as offline via
offline_mem_sections().

Also, after calling the "useless" undo_isolate_page_range() here, it
reaches the point of no returning by notifying MEM_OFFLINE. Those pages
will be marked as MIGRATE_MOVABLE again once onlining. In addition, fix
an incorrect comment along the way.

Signed-off-by: Qian Cai <cai@....pw>
---
 mm/memory_hotplug.c | 2 --
 mm/sparse.c         | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6b05576fb4ec..46017040b2f8 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1655,8 +1655,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	/* Ok, all of our target is isolated.
 	   We cannot do rollback at this point. */
 	offline_isolated_pages(start_pfn, end_pfn);
-	/* reset pagetype flags and makes migrate type to be MOVABLE */
-	undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
 	/* removal success */
 	adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages);
 	zone->present_pages -= offlined_pages;
diff --git a/mm/sparse.c b/mm/sparse.c
index 77a0554fa5bd..b3771f35a0ed 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -556,7 +556,7 @@ void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
 }

 #ifdef CONFIG_MEMORY_HOTREMOVE
-/* Mark all memory sections within the pfn range as online */
+/* Mark all memory sections within the pfn range as offline */
 void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
 {
 	unsigned long pfn;
-- 
2.17.2 (Apple Git-113)