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Thu, 5 Nov 2026 07:02:06 +0000 From: Mark Bundschuh To: CC: , , yangge , Baolin Wang , Barry Song <21cnbao@gmail.com>, David Hildenbrand , SeongJae Park , "Andrew Morton" , Mark Bundschuh Subject: [PATCH 5.10] mm: replace free hugepage folios after migration Date: Thu, 5 Nov 2026 07:01:50 +0000 Message-ID: <20261105070150.3093908-1-mkbund@amazon.com> X-Mailer: git-send-email 2.50.1 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: EX19D031UWA003.ant.amazon.com (10.13.139.47) To EX19D001UWA001.ant.amazon.com (10.13.138.214) From: yangge [ Upstream commit 04f13d241b8b146b23038bffd907cb8278391d07 ] My machine has 4 NUMA nodes, each equipped with 32GB of memory. I have configured each NUMA node with 16GB of CMA and 16GB of in-use hugetlb pages. The allocation of contiguous memory via cma_alloc() can fail probabilistically. When there are free hugetlb folios in the hugetlb pool, during the migration of in-use hugetlb folios, new folios are allocated from the free hugetlb pool. After the migration is completed, the old folios are released back to the free hugetlb pool instead of being returned to the buddy system. This can cause test_pages_isolated() check to fail, ultimately leading to the failure of cma_alloc(). Call trace: cma_alloc() __alloc_contig_migrate_range() // migrate in-use hugepage test_pages_isolated() __test_page_isolated_in_pageblock() PageBuddy(page) // check if the page is in buddy To address this issue, we introduce a function named replace_free_hugepage_folios(). This function will replace the hugepage in the free hugepage pool with a new one and release the old one to the buddy system. After the migration of in-use hugetlb pages is completed, we will invoke replace_free_hugepage_folios() to ensure that these hugepages are properly released to the buddy system. Following this step, when test_pages_isolated() is executed for inspection, it will successfully pass. Additionally, when alloc_contig_range() is used to migrate multiple in-use hugetlb pages, it can result in some in-use hugetlb pages being released back to the free hugetlb pool and subsequently being reallocated and used again. For example: [huge 0] [huge 1] To migrate huge 0, we obtain huge x from the pool. After the migration is completed, we return the now-freed huge 0 back to the pool. When it's time to migrate huge 1, we can simply reuse the now-freed huge 0 from the pool. As a result, when replace_free_hugepage_folios() is executed, it cannot release huge 0 back to the buddy system. To address this issue, we should prevent the reuse of isolated free hugepages during the migration process. Link: https://lkml.kernel.org/r/1734503588-16254-1-git-send-email-yangge1116@126.com Link: https://lkml.kernel.org/r/1736582300-11364-1-git-send-email-yangge1116@126.com Signed-off-by: yangge Cc: Baolin Wang Cc: Barry Song <21cnbao@gmail.com> Cc: David Hildenbrand Cc: SeongJae Park Signed-off-by: Andrew Morton [ 5.10: Take only the dequeue_huge_page_node_exact() hunk, so memory offline stops migrating huge pages back into the isolated range. ] Signed-off-by: Mark Bundschuh --- Without this, offlining a memory block holding mapped huge pages keeps migrating them back into the block until the offline is interrupted. Reproduced on arm64 on 5.10 and 6.12 (stock AL2023 6.12.113): the offline was still migrating after 60 s. With this patch on 5.10 it completes in 0.15 s with the data intact. Also sent for 5.10, 5.15, 6.1, 6.6 and 6.12. mm/hugetlb.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index b23c8b2699b5..4383de6fe621 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -41,6 +41,7 @@ #include #include #include +#include #include "internal.h" int hugetlb_max_hstate __read_mostly; @@ -1088,6 +1089,9 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid) if (PageHWPoison(page)) continue; + if (is_migrate_isolate_page(page)) + continue; + list_move(&page->lru, &h->hugepage_activelist); set_page_refcounted(page); ClearPageHugeFreed(page); -- 2.50.1