Re: [PATCH] btrfs: set flag to message when ratelimited

[Leo Martins <loemra.dev@gmail.com>]

On Tue, 17 Sep 2024 23:06, Naohiro Aota <Naohiro.Aota@wdc.com> wrote:
>On Tue, Sep 17, 2024 at 06:30:45PM GMT, David Sterba wrote:
>> On Fri, Sep 13, 2024 at 02:26:06PM -0700, Leo Martins wrote:
>> > Set RATELIMIT_MSG_ON_RELEASE flag to send a message when being
>> > ratelimited.
>> 
>> What does this really do? The documentation does not help either:
>> 
>> /* issue num suppressed message on exit */
>> 
>> > During some recent debugging not realizing that
>> > logs were being ratelimited caused some confusion so making
>> > sure there is a warning seems prudent.
>> 
>> So you can enable it only for debugging level.
>
>Adding my point, I often see btrfs_info() in btrfs_dump_space_info() is
>ratelimited and the info is incomplete, because it tries to print usage info
>about all the block groups. For that purpose, I don't think printing the
>number of suppressed lines helps.
>
>Instead, I'd prefer disabling rate limit for them, given that the messages
>are behind some debug flag (e.g, CONFIG_BTRFS_DEBUG and/or mount -o
>enospc_debug). So, how about adding btrfs_debug_info() which prints the
>message in INFO level without rate limitting?

When I previously sent this patch I thought that
RATELIMIT_MSG_ON_RELEASE flag caused a warning message to be printed
when ratelimited. This is true, however, a warning message is printed
regardless of whether this flag is enabled. When the flag is disabled
there is a printk_deferred [1] that will warn the user of the number
of callbacks that were suppressed. When the flag is enabled the warning
is instead printed when ratelimit_state_exit [2] is called which happens
on closing of /dev/kmsg. I now think that setting the flag isn't
necessary and instead I'll send out a different patch that implements
what Naohiro suggested.

[1] https://github.com/btrfs/linux/blob/21b136cc63d2a9ddd60d4699552b69c214b32964/lib/ratelimit.c#L56
[2] https://github.com/btrfs/linux/blob/21b136cc63d2a9ddd60d4699552b69c214b32964/include/linux/ratelimit.h#L31