linux-kernel - [PATCH] mm: hugetlb_vmemmap: simplify reset_struct

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Message-Id: <20220819035532.6189-1-songmuchun@bytedance.com>
Date:   Fri, 19 Aug 2022 11:55:32 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, songmuchun@...edance.com,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        muchun.song@...ux.dev
Subject: [PATCH] mm: hugetlb_vmemmap: simplify reset_struct_pages()

We can choose to copy three contiguous tail pages' content to the first three pages
instead of copying one by one to simplify the code and reduce code size from 229 bytes
to 63 bytes. The BUILD_BUG_ON() aims to avoid out-of-bounds accesses.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/hugetlb_vmemmap.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 76b2d03a0d8d..ba2a2596fb4e 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -265,11 +265,10 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
 
 static inline void reset_struct_pages(struct page *start)
 {
-	int i;
 	struct page *from = start + NR_RESET_STRUCT_PAGE;
 
-	for (i = 0; i < NR_RESET_STRUCT_PAGE; i++)
-		memcpy(start + i, from, sizeof(*from));
+	BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
+	memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
 }
 
 static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
-- 
2.11.0