linux-kernel - [PATCH v4 04/13] mm: khugepaged: __collapse_huge_page_swapin() use pte_offset_map_ro

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Message-Id: <69e1c4483c2d679d3e2c8446264e5878e5b52a97.1727148662.git.zhengqi.arch@bytedance.com>
Date: Tue, 24 Sep 2024 14:09:56 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: david@...hat.com,
	hughd@...gle.com,
	willy@...radead.org,
	muchun.song@...ux.dev,
	vbabka@...nel.org,
	akpm@...ux-foundation.org,
	rppt@...nel.org,
	vishal.moola@...il.com,
	peterx@...hat.com,
	ryan.roberts@....com,
	christophe.leroy2@...soprasteria.com
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v4 04/13] mm: khugepaged: __collapse_huge_page_swapin() use pte_offset_map_ro_nolock()

In __collapse_huge_page_swapin(), we just use the ptl for pte_same() check
in do_swap_page(). In other places, we directly use pte_offset_map_lock(),
so convert it to using pte_offset_map_ro_nolock().

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Muchun Song <muchun.song@...ux.dev>
---
 mm/khugepaged.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f9c39898eaff6..6498721d4783a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1011,7 +1011,11 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 		};
 
 		if (!pte++) {
-			pte = pte_offset_map_nolock(mm, pmd, address, &ptl);
+			/*
+			 * Here the ptl is only used to check pte_same() in
+			 * do_swap_page(), so readonly version is enough.
+			 */
+			pte = pte_offset_map_ro_nolock(mm, pmd, address, &ptl);
 			if (!pte) {
 				mmap_read_unlock(mm);
 				result = SCAN_PMD_NULL;
-- 
2.20.1