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Subject[PATCH v1 2/5] mm/memory_hotplug: enforce section alignment when onlining/offlining
onlining/offlining code works on whole sections, so let's enforce that.
Existing code only allows to add memory in memory block size. And only
whole memory blocks can be onlined/offlined. Memory blocks are always
aligned to sections, so this should not break anything.

online_pages/offline_pages will implicitly mark whole sections
online/offline, so the code really can only handle such granularities.

(especially offlining code cannot deal with pageblock_nr_pages but
theoretically only MAX_ORDER-1)

Signed-off-by: David Hildenbrand <>
mm/memory_hotplug.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 090cf474de87..30d2fa42b0bb 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -897,6 +897,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
struct memory_notify arg;
struct memory_block *mem;

+ return -EINVAL;
+ return -EINVAL;
* We can't use pfn_to_nid() because nid might be stored in struct page
* which is not yet initialized. Instead, we find nid from memory block.
@@ -1600,10 +1605,9 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
struct zone *zone;
struct memory_notify arg;

- /* at least, alignment against pageblock is necessary */
- if (!IS_ALIGNED(start_pfn, pageblock_nr_pages))
+ if (!IS_ALIGNED(start_pfn, PAGES_PER_SECTION))
return -EINVAL;
- if (!IS_ALIGNED(end_pfn, pageblock_nr_pages))
return -EINVAL;
/* This makes hotplug much easier...and readable.
we assume this for now. .*/
 \ /
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