linux-kernel - [PATCH v1 15/18] trace/events/page_ref: trace the raw page mapcount value

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Date: Tue,  9 Apr 2024 21:22:58 +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 15/18] trace/events/page_ref: trace the raw page mapcount value

We want to limit the use of page_mapcount() to the places where it is
absolutely necessary. We already trace raw page->refcount, raw page->flags
and raw page->mapping, and don't involve any folios. Let's also trace the
raw mapcount value that does not consider the entire mapcount of large
folios, and we don't add "1" to it.

When dealing with typed folios, this makes a lot more sense. ... and
it's for debugging purposes only either way.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/trace/events/page_ref.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/page_ref.h b/include/trace/events/page_ref.h
index 8a99c1cd417b..fe33a255b7d0 100644
--- a/include/trace/events/page_ref.h
+++ b/include/trace/events/page_ref.h
@@ -30,7 +30,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
 		__entry->pfn = page_to_pfn(page);
 		__entry->flags = page->flags;
 		__entry->count = page_ref_count(page);
-		__entry->mapcount = page_mapcount(page);
+		__entry->mapcount = atomic_read(&page->_mapcount);
 		__entry->mapping = page->mapping;
 		__entry->mt = get_pageblock_migratetype(page);
 		__entry->val = v;
@@ -79,7 +79,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
 		__entry->pfn = page_to_pfn(page);
 		__entry->flags = page->flags;
 		__entry->count = page_ref_count(page);
-		__entry->mapcount = page_mapcount(page);
+		__entry->mapcount = atomic_read(&page->_mapcount);
 		__entry->mapping = page->mapping;
 		__entry->mt = get_pageblock_migratetype(page);
 		__entry->val = v;
-- 
2.44.0