linux-kernel - [PATCH v2 1/3] mm: hugetlb: disable freeing vmemmap pages when struct page crosses page boundaries

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Message-Id: <20220302083758.32528-2-songmuchun@bytedance.com>
Date:   Wed,  2 Mar 2022 16:37:56 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     corbet@....net, mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2 1/3] mm: hugetlb: disable freeing vmemmap pages when struct page crosses page boundaries

If CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON is enabled and the size
of "struct page" is not power of two, we cannot optimize vmemmap pages
of HugeTLB pages. We should disable this feature in this case.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/hugetlb_vmemmap.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index b3118dba0518..836d1117f08b 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -121,6 +121,17 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 	if (!hugetlb_free_vmemmap_enabled())
 		return;
 
+	if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON) &&
+	    !is_power_of_2(sizeof(struct page))) {
+		/*
+		 * The hugetlb_free_vmemmap_enabled_key can be enabled when
+		 * CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON. It should
+		 * be disabled if "struct page" crosses page boundaries.
+		 */
+		static_branch_disable(&hugetlb_free_vmemmap_enabled_key);
+		return;
+	}
+
 	vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
 	/*
 	 * The head page is not to be freed to buddy allocator, the other tail
-- 
2.11.0