linux-kernel - [PATCH v3 1/8] mm: migrate: remove PageTransHuge check in numamigrate_isolate

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Message-ID: <20230913095131.2426871-2-wangkefeng.wang@huawei.com>
Date:   Wed, 13 Sep 2023 17:51:24 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <willy@...radead.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <ying.huang@...el.com>,
        <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: [PATCH v3 1/8] mm: migrate: remove PageTransHuge check in numamigrate_isolate_page()

The assert VM_BUG_ON_PAGE(order && !PageTransHuge(page), page) is
not very useful,

   1) for a tail/base page, order = 0, for a head page, the order > 0 &&
      PageTransHuge() is true
   2) there is a PageCompound() check and only base page is handled in
      do_numa_page(), and do_huge_pmd_numa_page() only handle PMD-mapped
      THP
   3) even though the page is a tail page, isolate_lru_page() will post
      a warning, and fail to isolate the page
   4) if large folio/pte-mapped THP migration supported in the future,
      we could migrate the entire folio if numa fault on a tail page

so just remove the check.

Suggested-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
---
 mm/migrate.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index b7fa020003f3..646d8ee7f102 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2483,8 +2483,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
 	int nr_pages = thp_nr_pages(page);
 	int order = compound_order(page);
 
-	VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
-
 	/* Do not migrate THP mapped by multiple processes */
 	if (PageTransHuge(page) && total_mapcount(page) > 1)
 		return 0;
-- 
2.27.0