linux-kernel - [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page

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Date:   Fri, 17 Dec 2021 12:30:41 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Donald Dutile <ddutile@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, David Hildenbrand <david@...hat.com>
Subject: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount()

Let's return early for hugetlb, which really only relies on the compound
mapcount so far and does not support PageDoubleMap() yet. Use the chance
to cleanup the file-THP case to make it easier to grasp. While at it, use
head_compound_mapcount().

This is a preparation for further changes.

Reviewed-by: Peter Xu <peterx@...hat.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/util.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 741ba32a43ac..3239e75c148d 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -732,15 +732,18 @@ int __page_mapcount(struct page *page)
 {
 	int ret;
 
-	ret = atomic_read(&page->_mapcount) + 1;
+	if (PageHuge(page))
+		return compound_mapcount(page);
 	/*
 	 * For file THP page->_mapcount contains total number of mapping
 	 * of the page: no need to look into compound_mapcount.
 	 */
-	if (!PageAnon(page) && !PageHuge(page))
-		return ret;
+	if (!PageAnon(page))
+		return atomic_read(&page->_mapcount) + 1;
+
+	ret = atomic_read(&page->_mapcount) + 1;
 	page = compound_head(page);
-	ret += atomic_read(compound_mapcount_ptr(page)) + 1;
+	ret += head_compound_mapcount(page);
 	if (PageDoubleMap(page))
 		ret--;
 	return ret;
-- 
2.31.1