linux-kernel - [PATCHv2 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced

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Date:   Fri,  3 Apr 2020 14:29:22 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>
Cc:     Zi Yan <ziy@...dia.com>, Yang Shi <yang.shi@...ux.alibaba.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv2 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced

__collapse_huge_page_swapin() check number of referenced PTE to decide
if the memory range is hot enough to justify swapin.

The problem is that it stops collapse altogether if there's not enough
referenced pages, not only swappingin.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative")
Reviewed-by: Zi Yan <ziy@...dia.com>
---
 mm/khugepaged.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 99bab7e4d05b..14d7afc90786 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -905,7 +905,8 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 	/* we only decide to swapin, if there is enough young ptes */
 	if (referenced < HPAGE_PMD_NR/2) {
 		trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
-		return false;
+		/* Do not block collapse, only skip swapping in */
+		return true;
 	}
 	vmf.pte = pte_offset_map(pmd, address);
 	for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
-- 
2.26.0