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From: "David Hildenbrand (Arm)" <david@kernel.org>
To: "Tejun Heo" <tj@kernel.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Shuah Khan" <skhan@linuxfoundation.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Lorenzo Stoakes" <ljs@kernel.org>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	"Vlastimil Babka" <vbabka@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Rik van Riel" <riel@surriel.com>, "Harry Yoo" <harry@kernel.org>,
	"Jann Horn" <jannh@google.com>,
	"Brendan Jackman" <jackmanb@google.com>,
	"Zi Yan" <ziy@nvidia.com>, "Pedro Falcato" <pfalcato@suse.de>,
	"Matthew Wilcox" <willy@infradead.org>
Cc: cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
	 linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	 linux-fsdevel@vger.kernel.org,
	"David Hildenbrand (Arm)" <david@kernel.org>
Subject: [PATCH RFC 05/13] fs/proc/task_mmu: remove mapcount comment in smaps_account()
Date: Sun, 12 Apr 2026 20:59:36 +0200	[thread overview]
Message-ID: <20260412-mapcount-v1-5-05e8dfab52e0@kernel.org> (raw)
In-Reply-To: <20260412-mapcount-v1-0-05e8dfab52e0@kernel.org>

Reading the mapcount is a usually a snapshot that can change immediately
afterwards, except when the folio is locked and the folio is unmapped.

For example, nothing stops other folio/page mappings that are not protected
through the same PTL from going away; the folio lock cannot prevent that
situation.

Let's just drop the comment.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 fs/proc/task_mmu.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 1e1572849fed..55b037768c60 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -968,11 +968,6 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
 		exclusive = !folio_maybe_mapped_shared(folio);
 	}
 
-	/*
-	 * We obtain a snapshot of the mapcount. Without holding the folio lock
-	 * this snapshot can be slightly wrong as we cannot always read the
-	 * mapcount atomically.
-	 */
 	for (i = 0; i < nr; i++, page++) {
 		unsigned long pss = PAGE_SIZE << PSS_SHIFT;
 

-- 
2.43.0



  parent reply	other threads:[~2026-04-12 19:00 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-12 18:59 [PATCH RFC 00/13] mm/rmap: support arbitrary folio mappings David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 01/13] mm/rmap: remove folio->_nr_pages_mapped David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 02/13] fs/proc/task_mmu: remove CONFIG_PAGE_MAPCOUNT handling for "mapmax" David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 03/13] fs/proc/page: remove CONFIG_PAGE_MAPCOUNT handling for kpagecount David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 04/13] fs/proc/task_mmu: remove CONFIG_PAGE_MAPCOUNT handling for PM_MMAP_EXCLUSIVE David Hildenbrand (Arm)
2026-04-12 18:59 ` David Hildenbrand (Arm) [this message]
2026-04-12 18:59 ` [PATCH RFC 06/13] fs/proc/task_mmu: remove CONFIG_PAGE_MAPCOUNT handling in smaps_account() David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 07/13] mm/rmap: remove CONFIG_PAGE_MAPCOUNT David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 08/13] mm: re-consolidate folio->_entire_mapcount David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 09/13] mm: move _large_mapcount to _mapcount in page[1] of a large folio David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 10/13] mm: re-consolidate folio->_pincount David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 11/13] mm/rmap: stop using the entire mapcount for hugetlb folios David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 12/13] mm/rmap: large mapcount interface cleanups David Hildenbrand (Arm)
2026-04-12 18:59 ` [PATCH RFC 13/13] mm/rmap: support arbitrary folio mappings David Hildenbrand (Arm)

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