Re: swapaccount= commandline option

[Michal Hocko <mhocko@suse.com>]

On Tue 13-02-24 08:01:37, Narcis Garcia wrote:
> El 12/2/24 a les 23:37, Yosry Ahmed ha escrit:
> > On Sun, Feb 11, 2024 at 1:33 AM Narcis Garcia <debianlists@actiu.net> wrote:
> > > 
> > > Hello,
> > > 
> > > I read this warning on Linux 6.1 boot:
> > > The swapaccount= commandline option is deprecated. Please report your
> > > usecase to linux-mm@kvack.org if you depend on this functionality.
> > > 
> > > And I want to know if this impacts on LinuX Containers (LXC) swap
> > > accounting.
> > 
> > swapaccount= was deprecated in the sense that it is always on now
> > (i.e. you cannot do swapaccount=0 anymore). I believe you are using
> > swapaccount=1 and want to make sure that swap accounting will still
> > work with v6.1, right?
> > 
> > This is the second question we have had about this message [1]. I
> > think we need to clarify the warning (and perhaps backport to stable
> > kernels).
> > 
> > [1]https://lore.kernel.org/linux-mm/2593755.Xrv9ptJ69j@sinistra.local/
> 
> 
> Thank you for answering this question, and sure this clarification is needed
> both in documentation and warning message.
> I've found deprecation message was commited on 26 Sep 2022.
> From what Linux version release, this deprecation is included?
> 
> I suggest this for setup_swap_account() code:
> pr_warn_once("The swapaccount= commandline option is deprecated. "
> 	"Swap accounting is always on. "
> 	"Please report your usecase to linux-mm@kvack.org if you "
> 	"depend on this functionality.\n");

Would it make more sense to warn only if somebody tries to disable the
swap accounting?
--- 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e4c8735e7c85..dec75eedf634 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7936,7 +7936,10 @@ 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. "
+	bool res;
+
+	if (kstrtobool(s, &res) || !res)
+		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");
 	return 1;
-- 
Michal Hocko
SUSE Labs