linux-kernel - [PATCH v2 7/8] mm: migrate: remove PageHead() check for HugeTLB in add_page_for

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Message-ID: <20230821115624.158759-8-wangkefeng.wang@huawei.com>
Date:   Mon, 21 Aug 2023 19:56:23 +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 v2 7/8] mm: migrate: remove PageHead() check for HugeTLB in add_page_for_migration()

There is some different between hugeTLB and THP behave when passed the
address of a tail page, for THP, it will migrate the entire THP page,
but for HugeTLB, it will return -EACCES, or -ENOENT before commit
e66f17ff7177 ("mm/hugetlb: take page table lock in follow_huge_pmd()"),

  -EACCES The page is mapped by multiple processes and can be moved
	  only if MPOL_MF_MOVE_ALL is specified.
  -ENOENT The page is not present.

But when check manual[1], both of the two errnos are not suitable, it
is better to keep the same behave between hugetlb and THP when passed
the address of a tail page, so let's just remove the PageHead() check
for HugeTLB.

[1] https://man7.org/linux/man-pages/man2/move_pages.2.html

Suggested-by: Mike Kravetz <mike.kravetz@...cle.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
---
 mm/migrate.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 73572d5a5cd4..e8c3fb8974f9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2093,10 +2093,8 @@ static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
 		goto out_putfolio;
 
 	if (folio_test_hugetlb(folio)) {
-		if (PageHead(page)) {
-			isolated = isolate_hugetlb(folio, pagelist);
-			err = isolated ? 1 : -EBUSY;
-		}
+		isolated = isolate_hugetlb(folio, pagelist);
+		err = isolated ? 1 : -EBUSY;
 	} else {
 		isolated = folio_isolate_lru(folio);
 		if (!isolated) {
-- 
2.41.0