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

[Balbir Singh]

On 11/12/25 10:50, Andrew Morton wrote:
> 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.

Thanks Steve and Andrew!

I've been looking at EVENT_CLASSES and looking for the savings you mentioned. I've not yet
finished my patch, I will resend it as soon as I have a new version

Balbir