Re: [PATCH] mm/migrate_device: Add tracepoints for debugging

[Andrew Morton]

On Mon, 10 Nov 2025 16:19:54 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Thu, 16 Oct 2025 16:46:19 +1100
> Balbir Singh <balbirs@xxxxxxxxxx> wrote:
> 
> > Add tracepoints for debugging device migration flow in migrate_device.c.
> > This is helpful in debugging how long migration took (time can be
> > tracked backwards from migrate_device_finalize to migrate_vma_setup).
> > 
> > A combination of these events along with existing thp:*, exceptions:*
> > and migrate:* is very useful for debugging issues related to
> > migration.
> > 
>
> ...
>
> >        hmm-tests-855   [002]    50.042800: set_migration_pmd:    addr=7f2908a00000, pmd=dfffffffd39ffe00
> >        hmm-tests-855   [002]    50.062345: remove_migration_pmd: addr=7f2908a00000, pmd=efffffe00403fe00
> 
> Each TRACE_EVENT() is equivalent to:
> 
> DECLARE_EVENT_CLASS(event, ...)
> DEFINE_EVENT(event, event, ...)
> 
> Where a class is around 4-5K in size, and the DEFINE_EVENT is between
> 500 and 1k in size.
> 
> By using a single DECLARE_EVENT_CLASS() for multiple events, you can save
> several thousands of bytes of memory.

Thanks for the detailed review.  I'll drop this version of the patch.