linux-kernel - Re: [PATCH 3/3] mm/damon/dbgfs: print DAMON debugfs interface deprecation message

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Message-ID: <655f44cf-1d39-c2c1-1a93-d8eec39064b4@infradead.org>
Date:   Thu, 9 Feb 2023 20:32:21 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/damon/dbgfs: print DAMON debugfs interface
 deprecation message

Hi,

On 2/9/23 20:24, SeongJae Park wrote:
> Hi Randy,
> 
> On Thu, 9 Feb 2023 19:26:43 -0800 Randy Dunlap <rdunlap@...radead.org> wrote:
> 
>> Hi,
>>
>> On 2/9/23 11:20, SeongJae Park wrote:
>>> DAMON debugfs interface has announced to be deprecated after >v5.15 LTS
>>> kernel is released.  And, v6.1.y has announced to be an LTS[1].
>>>
>>> Though the announcement was there for a while, some people might not
>>> noticed that so far.  Also, some users could depend on it and have
>>> problems at  movng to the alternative (DAMON sysfs interface).
>>>
>>> For such cases, warn DAMON debugfs interface deprecation with contacts
>>> to ask helps when any DAMON debugfs interface file is opened.
>>>
>>> [1] https://git.kernel.org/pub/scm/docs/kernel/website.git/commit/?id=332e9121320bc7461b2d3a79665caf153e51732c
>>>
>>> Signed-off-by: SeongJae Park <sj@...nel.org>
>>> ---
>>>  mm/damon/dbgfs.c | 16 ++++++++++++++++
>>>  1 file changed, 16 insertions(+)
>>>
>>> diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
>>> index b3f454a5c682..e551a20b35e3 100644
>>> --- a/mm/damon/dbgfs.c
>>> +++ b/mm/damon/dbgfs.c
>>> @@ -20,6 +20,11 @@ static int dbgfs_nr_ctxs;
>>>  static struct dentry **dbgfs_dirs;
>>>  static DEFINE_MUTEX(damon_dbgfs_lock);
>>>  
>>> +static void damon_dbgfs_warn_deprecation(void)
>>> +{
>>> +	pr_warn_once("DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).  If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");
>>> +}
>>
>> Line length of 234 is a bit over the limit.
>> I think it would be OK to split it at the end of the first sentence, like:
>>
>> 	pr_warn_once("DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).\n");
>> 	pr_warn_once("If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");
>>
>> or would that [2 pr_warn_once() calls] not work for some reason?
>>
>> Or even:
>>
>> 	pr_warn_once(
>> "DAMON debugfs interface is deprecated, so users should move to the sysfs interface (DAMON_SYSFS).\n");
>> 	pr_warn_once(
>> "If you depend on this and cannot move, please report your usecase to damon@...ts.linux.dev and linux-mm@...ck.org.\n");
>>
>> although some people might gag at that one.
> 
> Thank you for your opinion.
> 
> I considered that, but I was worrying if some other messages come between those
> two separated messages.

I see.

> 
> What do you think about breaking the string like below?  I first tried to do so
> like memcg hierarchy[1], but ended up to this version because of checkpatch.pl
> outputs[2].  However, if others doesn't care, I think this is ok.

It's OK to ignore checkpatch sometimes. :)

> 
> 	pr_warn_once("DAMON debugfs interface is deprecated, "
> 		     "so users should move DAMON_SYSFS. If you depend on this "
> 		     "and cannot move, please report your usecase to "
> 		     "damon@...ts.linux.dev and linux-mm@...ck.org.\n");
> 
> If breaking user-visible string is not ok, maybe we could make it as short as
> your above example.
> 
>  	pr_warn_once("DAMON_DBGFS is deprecated; please contact to damon@...ts.linux.dev and linux-mm@...ck.org if you depend on it.\n");
> 
> May I ask your opinion?

I'm OK with either one of these, but I prefer your first example over the second one.

> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memcontrol.c?h=v6.1#n3643
> [2] https://docs.kernel.org/process/coding-style.html#breaking-long-lines-and-strings

Thanks.
-- 
~Randy