On Feb 15, 2025, at 15:20, yangge1116@xxxxxxx wrote:
From: Ge Yang <yangge1116@xxxxxxx>
Since the introduction of commit b65d4adbc0f0 ("mm: hugetlb: defer
freeing
of HugeTLB pages"), 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 hugepage folios, these in-use hugepage folios need to be
migrated
to another location. When there are no available hugepage folios in the
free HugeTLB pool during the migration of in-use HugeTLB pages, new
folios
are allocated from the buddy system. A temporary state is set on the
newly
allocated folio. Upon completion of the hugepage 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 hugepage
->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_hugepage_folios_freed(). This function ensures that the
hugepage
folios are properly released back to the buddy system after their
migration
is completed. By invoking wait_for_hugepage_folios_freed() before
calling
PageBuddy(), we ensure that PageBuddy() will succeed.
Fixes: b65d4adbc0f0 ("mm: hugetlb: defer freeing of HugeTLB pages")
Signed-off-by: Ge Yang <yangge1116@xxxxxxx>
---
V2:
- flush all folios at once suggested by David
include/linux/hugetlb.h | 5 +++++
mm/hugetlb.c | 8 ++++++++
mm/page_isolation.c | 10 ++++++++++
3 files changed, 23 insertions(+)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 6c6546b..04708b0 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -697,6 +697,7 @@ bool hugetlb_bootmem_page_zones_valid(int nid,
struct huge_bootmem_page *m);
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_hugepage_folios_freed(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,
@@ -1092,6 +1093,10 @@ static inline int
replace_free_hugepage_folios(unsigned long start_pfn,
return 0;
}
+static inline void wait_for_hugepage_folios_freed(void)
+{
+}
+
static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct
*vma,
unsigned long addr,
bool cow_from_owner)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 30bc34d..36dd3e4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2955,6 +2955,14 @@ int replace_free_hugepage_folios(unsigned long
start_pfn, unsigned long end_pfn)
return ret;
}
+void wait_for_hugepage_folios_freed(void)
