Re: [PATCH 00/14] xfs: Remove unused trace events

[Darrick J. Wong]

On Thu, Jun 12, 2025 at 05:24:05PM -0400, Steven Rostedt wrote:
> 
> Trace events take up to 5K in memory for text and meta data. I have code that

Under what circumstances do they eat up that much memory?  And is that
per-class?  Or per-tracepoint?

> will trigger a warning when it detects unused tracepoints. The XFS file
> system contains many events that are not called. Most of them used to be called
> but due to code refactoring the calls were removed but the trace events stayed
> behind.
> 
> Some events were added but never used. If they were recent, I just reported
> them, but if they were older, this series simply removes them.

TBH it'd be really nice if there was /something/ in the build path that
would complain about disused tracepoints.  I often put in tracepoints
while developing a feature, then the code gets massively rewritten
during review, and none of us remember to rip out the orphaned traces...

> One is called only when CONFIG_COMPACT is defined, so an #ifdef was placed
> around it.
> 
> A couple are only called in #if 0 code (left as a reminder to fix it), so
> those events are wrapped by a #if 0 as well (with a comment).
> 
> Finally, one event is supposed to be a trace event class, but was created with
> the TRACE_EVENT() macro and not the DECLARE_EVENT_CLASS() macro. This works
> because a TRACE_EVENT() is simply a DECLARE_EVENT_CLASS() and DEFINE_EVENT()
> where the class and event have the same name. But as this was a mistake, the
> event created should not exist.
> 
> Each patch is a stand alone patch. If you ack them, I can take them in my
> tree, or if you want, you can take them. I may be adding the warning code to
> linux-next near the end of the cycle, so it would be good to have this cleaned
> up before hand. As this is removing dead code, it may be even OK to send them
> to Linus as a fix.

...oh, you /do/ have a program and it's coming down the pipeline.
Excellent <tents fingers>. :)

--D

> 
> Steven Rostedt (14):
>       xfs: tracing; Remove unused event xfs_reflink_cow_found
>       xfs: Remove unused trace event xfs_attr_remove_iter_return
>       xfs: Remove unused event xlog_iclog_want_sync
>       xfs: Remove unused event xfs_ioctl_clone
>       xfs: Remove unused xfs_reflink_compare_extents events
>       xfs: Remove unused trace event xfs_attr_rmtval_set
>       xfs: ifdef out unused xfs_attr events
>       xfs: Remove unused event xfs_attr_node_removename
>       xfs: Remove unused event xfs_alloc_near_error
>       xfs: Remove unused event xfs_alloc_near_nominleft
>       xfs: Remove unused event xfs_pagecache_inval
>       xfs: Remove usused xfs_end_io_direct events
>       xfs: Only create event xfs_file_compat_ioctl when CONFIG_COMPAT is configure
>       xfs: Change xfs_xattr_class from a TRACE_EVENT() to DECLARE_EVENT_CLASS()
> 
> ----
>  fs/xfs/scrub/trace.h |  2 +-
>  fs/xfs/xfs_trace.h   | 72 ++++++----------------------------------------------
>  2 files changed, 9 insertions(+), 65 deletions(-)
>