linux-kernel - [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

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Date: Tue, 13 Feb 2024 03:16:34 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...nel.org>,
	Shakeel Butt <shakeelb@...gle.com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jonas Schäfer <jonas@...licki.name>,
	Narcis Garcia <debianlists@...iu.net>,
	Yosry Ahmed <yosryahmed@...gle.com>
Subject: [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

The swapaccount deprecation warning is throwing false positives. Since
we deprecated the knob and defaulted to enabling, the only reports
we've been getting are from folks that set swapaccount=1. While this
is a nice affirmation that always-enabling was the right choice, we
certainly don't want to warn when users request the supported mode.

Only warn when disabling is requested, and clarify the warning.

Fixes: b25806dcd3d5 ("mm: memcontrol: deprecate swapaccounting=0 mode")
Cc: stable@...r.kernel.org
Reported-by: "Jonas Schäfer" <jonas@...licki.name>
Reported-by: Narcis Garcia <debianlists@...iu.net>
Suggested-by: Yosry Ahmed <yosryahmed@...gle.com>
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/memcontrol.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1ed40f9d3a27..107ec5d36819 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7971,9 +7971,13 @@ bool mem_cgroup_swap_full(struct folio *folio)
 
 static int __init setup_swap_account(char *s)
 {
-	pr_warn_once("The swapaccount= commandline option is deprecated. "
-		     "Please report your usecase to linux-mm@...ck.org if you "
-		     "depend on this functionality.\n");
+	bool res;
+
+	if (!kstrtobool(s, &res) && !res)
+		pr_warn_once("The swapaccount=0 commdandline option is deprecated "
+			     "in favor of configuring swap control via cgroupfs. "
+			     "Please report your usecase to linux-mm@...ck.org if you "
+			     "depend on this functionality.\n");
 	return 1;
 }
 __setup("swapaccount=", setup_swap_account);
-- 
2.43.0