linux-kernel - [PATCH] replace free hugepage folios after migration

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Message-Id: <1734503588-16254-1-git-send-email-yangge1116@126.com>
Date: Wed, 18 Dec 2024 14:33:08 +0800
From: yangge1116@....com
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	21cnbao@...il.com,
	david@...hat.com,
	baolin.wang@...ux.alibaba.com,
	muchun.song@...ux.dev,
	liuzixing@...on.cn,
	yangge <yangge1116@....com>
Subject: [PATCH] replace free hugepage folios after migration

From: yangge <yangge1116@....com>

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 the
cma_alloc() function can fail probabilistically.

The cma_alloc() function may fail if it sees an in-use hugetlb page
within the allocation range, even if that page has already been
migrated. When in-use hugetlb pages are migrated, they may simply
be released back into the free hugepage pool instead of being
returned to the buddy system. This can cause the
test_pages_isolated() function check to fail, ultimately leading
to the failure of the cma_alloc() function:
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 will add 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 the replace_free_hugepage_folios()
function to ensure that these hugepages are properly released to
the buddy system. Following this step, when the test_pages_isolated()
function is executed for inspection, it will successfully pass.

Signed-off-by: yangge <yangge1116@....com>
---
 include/linux/hugetlb.h |  6 ++++++
 mm/hugetlb.c            | 37 +++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c         | 13 ++++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index ae4fe86..7d36ac8 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -681,6 +681,7 @@ 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);
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 				unsigned long addr, int avoid_reserve);
 struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
@@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page,
 	return -ENOMEM;
 }
 
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
+{
+	return 0;
+}
+
 static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 					   unsigned long addr,
 					   int avoid_reserve)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8e1db80..a099c54 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
 	return ret;
 }
 
+/*
+ *  replace_free_hugepage_folios - Replace free hugepage folios in a given pfn
+ *  range with new folios.
+ *  @stat_pfn: start pfn of the given pfn range
+ *  @end_pfn: end pfn of the given pfn range
+ *  Returns 0 on success, otherwise negated error.
+ */
+int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
+{
+	struct hstate *h;
+	struct folio *folio;
+	int ret = 0;
+
+	LIST_HEAD(isolate_list);
+
+	while (start_pfn < end_pfn) {
+		folio = pfn_folio(start_pfn);
+		if (folio_test_hugetlb(folio)) {
+			h = folio_hstate(folio);
+		} else {
+			start_pfn++;
+			continue;
+		}
+
+		if (!folio_ref_count(folio)) {
+			ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list);
+			if (ret)
+				break;
+
+			putback_movable_pages(&isolate_list);
+		}
+		start_pfn++;
+	}
+
+	return ret;
+}
+
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 				    unsigned long addr, int avoid_reserve)
 {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dde19db..1dcea28 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
 	ret = __alloc_contig_migrate_range(&cc, start, end, migratetype);
 	if (ret && ret != -EBUSY)
 		goto done;
-	ret = 0;
+
+	/*
+	 * When in-use hugetlb pages are migrated, they may simply be
+	 * released back into the free hugepage pool instead of being
+	 * returned to the buddy system. After the migration of in-use
+	 * huge pages is completed, we will invoke the
+	 * replace_free_hugepage_folios() function to ensure that
+	 * these hugepages are properly released to the buddy system.
+	 */
+	ret = replace_free_hugepage_folios(start, end);
+	if (ret)
+		goto done;
 
 	/*
 	 * Pages from [start, end) are within a pageblock_nr_pages
-- 
2.7.4