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

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

[Johannes Weiner]

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@vger.kernel.org
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>
---
 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@kvack.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@kvack.org if you "
+			     "depend on this functionality.\n");
 	return 1;
 }
 __setup("swapaccount=", setup_swap_account);
-- 
2.43.0

Re: [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

[Yosry Ahmed]

On Tue, Feb 13, 2024 at 12:16 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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@vger.kernel.org
> 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>

> ---
>  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@kvack.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@kvack.org if you "
> +                            "depend on this functionality.\n");

This line is surely getting long, but I see other similar instances so
I guess that's okay.

>         return 1;
>  }
>  __setup("swapaccount=", setup_swap_account);
> --
> 2.43.0
>

Re: [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

[Michal Hocko]

On Tue 13-02-24 03:16:34, Johannes Weiner wrote:
> 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@vger.kernel.org
> 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>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  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@kvack.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@kvack.org if you "
> +			     "depend on this functionality.\n");
>  	return 1;
>  }
>  __setup("swapaccount=", setup_swap_account);
> -- 
> 2.43.0

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

[Shakeel Butt]

On Tue, Feb 13, 2024 at 12:16 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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@vger.kernel.org
> 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>

Acked-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH] mm: memcontrol: clarify swapaccount=0 deprecation warning

[Michal Koutný]

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On Tue, Feb 13, 2024 at 03:16:34AM -0500, Johannes Weiner <hannes@cmpxchg.org> wrote:
> 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.

But shouldn't such users be still warned about effectively unused option?
I think `return 0;` from the param handler should ensure that.


> +	if (!kstrtobool(s, &res) && !res)
> +		pr_warn_once("The swapaccount=0 commdandline option is deprecated "
                                                commandline

Regards,
Michal

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