linux-kernel - [PATCH RFC v2 8/9] mm/huge_memory: remove stale page_trans_huge

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Date:   Wed, 26 Jan 2022 10:55:56 +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>,
        Liang Zhang <zhangliang5@...wei.com>, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH RFC v2 8/9] mm/huge_memory: remove stale page_trans_huge_mapcount()

All users are gone, let's remove it.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/mm.h |  5 -----
 mm/huge_memory.c   | 48 ----------------------------------------------
 2 files changed, 53 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e1a84b1e6787..df6b34d66a9b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -820,16 +820,11 @@ static inline int page_mapcount(struct page *page)
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int total_mapcount(struct page *page);
-int page_trans_huge_mapcount(struct page *page);
 #else
 static inline int total_mapcount(struct page *page)
 {
 	return page_mapcount(page);
 }
-static inline int page_trans_huge_mapcount(struct page *page)
-{
-	return page_mapcount(page);
-}
 #endif
 
 static inline struct page *virt_to_head_page(const void *x)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b6ba88a98266..863c933b3b1e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2529,54 +2529,6 @@ int total_mapcount(struct page *page)
 	return ret;
 }
 
-/*
- * This calculates accurately how many mappings a transparent hugepage
- * has (unlike page_mapcount() which isn't fully accurate). This full
- * accuracy is primarily needed to know if copy-on-write faults can
- * reuse the page and change the mapping to read-write instead of
- * copying them. At the same time this returns the total_mapcount too.
- *
- * The function returns the highest mapcount any one of the subpages
- * has. If the return value is one, even if different processes are
- * mapping different subpages of the transparent hugepage, they can
- * all reuse it, because each process is reusing a different subpage.
- *
- * The total_mapcount is instead counting all virtual mappings of the
- * subpages. If the total_mapcount is equal to "one", it tells the
- * caller all mappings belong to the same "mm" and in turn the
- * anon_vma of the transparent hugepage can become the vma->anon_vma
- * local one as no other process may be mapping any of the subpages.
- *
- * It would be more accurate to replace page_mapcount() with
- * page_trans_huge_mapcount(), however we only use
- * page_trans_huge_mapcount() in the copy-on-write faults where we
- * need full accuracy to avoid breaking page pinning, because
- * page_trans_huge_mapcount() is slower than page_mapcount().
- */
-int page_trans_huge_mapcount(struct page *page)
-{
-	int i, ret;
-
-	/* hugetlbfs shouldn't call it */
-	VM_BUG_ON_PAGE(PageHuge(page), page);
-
-	if (likely(!PageTransCompound(page)))
-		return atomic_read(&page->_mapcount) + 1;
-
-	page = compound_head(page);
-
-	ret = 0;
-	for (i = 0; i < thp_nr_pages(page); i++) {
-		int mapcount = atomic_read(&page[i]._mapcount) + 1;
-		ret = max(ret, mapcount);
-	}
-
-	if (PageDoubleMap(page))
-		ret -= 1;
-
-	return ret + compound_mapcount(page);
-}
-
 /* Racy check whether the huge page can be split */
 bool can_split_huge_page(struct page *page, int *pextra_pins)
 {
-- 
2.34.1