On 09/05/2016 04:59 AM, Li Zhong wrote:
Commit 394e31d2c introduced new_node_page() for memory hotplug.
In new_node_page(), the nid is cleared before calling __alloc_pages_nodemask().
But if it is the only node of the system,
So the use case is that we are partially offlining the only online node?
and the first round allocation fails,
it will not be able to get memory from an empty nodemask, and trigger oom.
Hmm triggering OOM due to empty nodemask sounds like a wrong thing to do. CCing
some OOM experts for insight. Also OOM is skipped for __GFP_THISNODE
allocations, so we might also consider the same for nodemask-constrained
allocations?
The patch checks whether it is the last node on the system, and if it is, then
don't clear the nid in the nodemask.
I'd rather see the allocation not OOM, and rely on the fallback in
new_node_page() that doesn't have nodemask. But I suspect it might also make
sense to treat empty nodemask as something unexpected and put some WARN_ON
(instead of OOM) in the allocator.
Reported-by: John Allen <jallen@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Fixes: 394e31d2ceb4 ("mem-hotplug: alloc new page from a nearest neighbor node
when mem-offline")
---
mm/memory_hotplug.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 41266dc..b58906b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1567,7 +1567,9 @@ static struct page *new_node_page(struct page *page, unsigned long private,
return alloc_huge_page_node(page_hstate(compound_head(page)),
next_node_in(nid, nmask));
- node_clear(nid, nmask);
+ if (nid != next_node_in(nid, nmask))
+ node_clear(nid, nmask);
+
if (PageHighMem(page)
|| (zone_idx(page_zone(page)) == ZONE_MOVABLE))
gfp_mask |= __GFP_HIGHMEM;
--
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