linux-kernel - [PATCH v1 10/18] mm/page_alloc: use folio_mapped() in __alloc_contig_migrate

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Date: Tue,  9 Apr 2024 21:22:53 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-doc@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-sh@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Peter Xu <peterx@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Yang Shi <shy828301@...il.com>,
	Zi Yan <ziy@...dia.com>,
	Jonathan Corbet <corbet@....net>,
	Hugh Dickins <hughd@...gle.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Naoya Horiguchi <naoya.horiguchi@....com>,
	Richard Chang <richardycc@...gle.com>
Subject: [PATCH v1 10/18] mm/page_alloc: use folio_mapped() in __alloc_contig_migrate_range()

We want to limit the use of page_mapcount() to the places where it is
absolutely necessary.

For tracing purposes, we use page_mapcount() in
__alloc_contig_migrate_range(). Adding that mapcount to total_mapped sounds
strange: total_migrated and total_reclaimed would count each page only
once, not multiple times.

But then, isolate_migratepages_range() adds each folio only once to the
list. So for large folios, we would query the mapcount of the
first page of the folio, which doesn't make too much sense for large
folios.

Let's simply use folio_mapped() * folio_nr_pages(), which makes more
sense as nr_migratepages is also incremented by the number of pages in
the folio in case of successful migration.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/page_alloc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 393366d4a704..40fc0f60e021 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6389,8 +6389,12 @@ int __alloc_contig_migrate_range(struct compact_control *cc,
 
 		if (trace_mm_alloc_contig_migrate_range_info_enabled()) {
 			total_reclaimed += nr_reclaimed;
-			list_for_each_entry(page, &cc->migratepages, lru)
-				total_mapped += page_mapcount(page);
+			list_for_each_entry(page, &cc->migratepages, lru) {
+				struct folio *folio = page_folio(page);
+
+				total_mapped += folio_mapped(folio) *
+						folio_nr_pages(folio);
+			}
 		}
 
 		ret = migrate_pages(&cc->migratepages, alloc_migration_target,
-- 
2.44.0