linux-kernel - [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages

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Message-Id: <20240626024924.1155558-3-ranxiaokai627@163.com>
Date: Wed, 26 Jun 2024 02:49:24 +0000
From: ran xiaokai <ranxiaokai627@....com>
To: akpm@...ux-foundation.org,
	willy@...radead.org
Cc: vbabka@...e.cz,
	svetly.todorov@...verge.com,
	ran.xiaokai@....com.cn,
	baohua@...nel.org,
	ryan.roberts@....com,
	peterx@...hat.com,
	ziy@...dia.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH 2/2] kpageflags: fix wrong KPF_THP on non-pmd-mappable compound pages

From: Ran Xiaokai <ran.xiaokai@....com.cn>

KPF_COMPOUND_HEAD and KPF_COMPOUND_TAIL are set on "common" compound
pages, which means of any order, but KPF_THP should only be set
when the folio is a 2M pmd mappable THP. Since commit 19eaf44954df
("mm: thp: support allocation of anonymous multi-size THP"),
multiple orders of folios can be allocated and mapped to userspace,
so the folio_test_large() check is not sufficient here,
replace it with folio_test_pmd_mappable() to fix this.

Also kpageflags is not only for userspace memory but for all valid pfn
pages,including slab pages or drivers used pages, so the PG_lru and
is_anon check are unnecessary here.

Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
---
 fs/proc/page.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 2fb64bdb64eb..3e7b70449c2f 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -146,19 +146,13 @@ u64 stable_page_flags(const struct page *page)
 		u |= kpf_copy_bit(k, KPF_COMPOUND_HEAD, PG_head);
 	else
 		u |= 1 << KPF_COMPOUND_TAIL;
+
 	if (folio_test_hugetlb(folio))
 		u |= 1 << KPF_HUGE;
-	/*
-	 * We need to check PageLRU/PageAnon
-	 * to make sure a given page is a thp, not a non-huge compound page.
-	 */
-	else if (folio_test_large(folio)) {
-		if ((k & (1 << PG_lru)) || is_anon)
-			u |= 1 << KPF_THP;
-		else if (is_huge_zero_folio(folio)) {
+	else if (folio_test_pmd_mappable(folio)) {
+		u |= 1 << KPF_THP;
+		if (is_huge_zero_folio(folio))
 			u |= 1 << KPF_ZERO_PAGE;
-			u |= 1 << KPF_THP;
-		}
 	} else if (is_zero_pfn(page_to_pfn(page)))
 		u |= 1 << KPF_ZERO_PAGE;
 
-- 
2.15.2