linux-kernel - [PATCH 2/7] mm/khugepaged: stop swapping in page when VM_FAULT

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Message-ID: <20220611084731.55155-3-linmiaohe@huawei.com>
Date:   Sat, 11 Jun 2022 16:47:26 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <aarcange@...hat.com>, <willy@...radead.org>, <vbabka@...e.cz>,
        <dhowells@...hat.com>, <neilb@...e.de>, <apopple@...dia.com>,
        <david@...hat.com>, <surenb@...gle.com>, <peterx@...hat.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 2/7] mm/khugepaged: stop swapping in page when VM_FAULT_RETRY occurs

When do_swap_page returns VM_FAULT_RETRY, we do not retry here and thus
swap entry will remain in pagetable. This will result in later failure.
So stop swapping in pages in this case to save cpu cycles.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/khugepaged.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 73570dfffcec..a8adb2d1e9c6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1003,19 +1003,16 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 		swapped_in++;
 		ret = do_swap_page(&vmf);
 
-		/* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
+		/*
+		 * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
+		 * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
+		 * we do not retry here and swap entry will remain in pagetable
+		 * resulting in later failure.
+		 */
 		if (ret & VM_FAULT_RETRY) {
 			mmap_read_lock(mm);
-			if (hugepage_vma_revalidate(mm, haddr, &vma)) {
-				/* vma is no longer available, don't continue to swapin */
-				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
-				return false;
-			}
-			/* check if the pmd is still valid */
-			if (mm_find_pmd(mm, haddr) != pmd) {
-				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
-				return false;
-			}
+			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+			return false;
 		}
 		if (ret & VM_FAULT_ERROR) {
 			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
-- 
2.23.0