mm: memcontrol: clarify swapaccount=0 deprecation warning

commit 118642d7f606fc9b9c92ee611275420320290ffb upstream.

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.

[colin.i.king@gmail.com: spelling: "commdandline" -> "commandline"]
Link: https://lkml.kernel.org/r/20240215090544.1649201-1-colin.i.king@gmail.com
Link: https://lkml.kernel.org/r/20240213081634.3652326-1-hannes@cmpxchg.org
Fixes: b25806dcd3d5 ("mm: memcontrol: deprecate swapaccounting=0 mode")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reported-by: "Jonas Schäfer" <jonas@wielicki.name>
Reported-by: Narcis Garcia <debianlists@actiu.net>
Suggested-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9da98e3e71cfed84f1de91b1d7892d8879344928..4570d3e315cf15f7e2fe95515c78c102c9e43071 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7517,9 +7517,13 @@ 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@kvack.org if you "
-                    "depend on this functionality.\n");
+       bool res;
+
+       if (!kstrtobool(s, &res) && !res)
+               pr_warn_once("The swapaccount=0 commandline option is deprecated "
+                            "in favor of configuring swap control via cgroupfs. "
+                            "Please report your usecase to linux-mm@kvack.org if you "
+                            "depend on this functionality.\n");
        return 1;
 }
 __setup("swapaccount=", setup_swap_account);