The patch titled Subject: mm/hugetlb: wait for hugetlb folios to be freed has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-wait-for-hugetlb-folios-to-be-freed.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ge Yang yangge1116@126.com Subject: mm/hugetlb: wait for hugetlb folios to be freed Date: Wed, 19 Feb 2025 11:46:44 +0800

Since the introduction of commit c77c0a8ac4c52 ("mm/hugetlb: defer freeing of huge pages if in non-task context"), which supports deferring the freeing of hugetlb pages, the allocation of contiguous memory through cma_alloc() may fail probabilistically.

In the CMA allocation process, if it is found that the CMA area is occupied by in-use hugetlb folios, these in-use hugetlb folios need to be migrated to another location. When there are no available hugetlb folios in the free hugetlb pool during the migration of in-use hugetlb folios, new folios are allocated from the buddy system. A temporary state is set on the newly allocated folio. Upon completion of the hugetlb folio migration, the temporary state is transferred from the new folios to the old folios. Normally, when the old folios with the temporary state are freed, it is directly released back to the buddy system. However, due to the deferred freeing of hugetlb pages, the PageBuddy() check fails, ultimately leading to the failure of cma_alloc().

Here is a simplified call trace illustrating the process: cma_alloc() ->__alloc_contig_migrate_range() // Migrate in-use hugetlb folios ->unmap_and_move_huge_page() ->folio_putback_hugetlb() // Free old folios ->test_pages_isolated() ->__test_page_isolated_in_pageblock() ->PageBuddy(page) // Check if the page is in buddy

To resolve this issue, we have implemented a function named wait_for_freed_hugetlb_folios(). This function ensures that the hugetlb folios are properly released back to the buddy system after their migration is completed. By invoking wait_for_freed_hugetlb_folios() before calling PageBuddy(), we ensure that PageBuddy() will succeed.

Link: https://lkml.kernel.org/r/1739936804-18199-1-git-send-email-yangge1116@126.c... Fixes: c77c0a8ac4c52 ("mm/hugetlb: defer freeing of huge pages if in non-task context") Signed-off-by: Ge Yang yangge1116@126.com Reviewed-by: Muchun Song muchun.song@linux.dev Acked-by: David Hildenbrand david@redhat.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song 21cnbao@gmail.com Cc: Oscar Salvador osalvador@suse.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/hugetlb.h | 5 +++++ mm/hugetlb.c | 8 ++++++++ mm/page_isolation.c | 10 ++++++++++ 3 files changed, 23 insertions(+)

--- a/include/linux/hugetlb.h~mm-hugetlb-wait-for-hugetlb-folios-to-be-freed +++ a/include/linux/hugetlb.h @@ -682,6 +682,7 @@ struct huge_bootmem_page {

int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list); int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn); +void wait_for_freed_hugetlb_folios(void); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, bool cow_from_owner); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, @@ -1066,6 +1067,10 @@ static inline int replace_free_hugepage_ return 0; }

+static inline void wait_for_freed_hugetlb_folios(void) +{ +} + static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, bool cow_from_owner) --- a/mm/hugetlb.c~mm-hugetlb-wait-for-hugetlb-folios-to-be-freed +++ a/mm/hugetlb.c @@ -2943,6 +2943,14 @@ int replace_free_hugepage_folios(unsigne return ret; }

+void wait_for_freed_hugetlb_folios(void) +{ + if (llist_empty(&hpage_freelist)) + return; + + flush_work(&free_hpage_work); +} + typedef enum { /* * For either 0/1: we checked the per-vma resv map, and one resv --- a/mm/page_isolation.c~mm-hugetlb-wait-for-hugetlb-folios-to-be-freed +++ a/mm/page_isolation.c @@ -608,6 +608,16 @@ int test_pages_isolated(unsigned long st int ret;

/* + * Due to the deferred freeing of hugetlb folios, the hugepage folios may + * not immediately release to the buddy system. This can cause PageBuddy() + * to fail in __test_page_isolated_in_pageblock(). To ensure that the + * hugetlb folios are properly released back to the buddy system, we + * invoke the wait_for_freed_hugetlb_folios() function to wait for the + * release to complete. + */ + wait_for_freed_hugetlb_folios(); + + /* * Note: pageblock_nr_pages != MAX_PAGE_ORDER. Then, chunks of free * pages are not aligned to pageblock_nr_pages. * Then we just check migratetype first. _

Patches currently in -mm which might be from yangge1116@126.com are

mm-hugetlb-wait-for-hugetlb-folios-to-be-freed.patch