Re: [PATCH -V2] /proc/PID/smaps: Add PMD migration entry parsing

["Huang\, Ying" <ying.huang@intel.com>]

Michal Hocko <mhocko@kernel.org> writes:

> On Thu 02-04-20 16:10:29, Huang, Ying wrote:
>> Michal Hocko <mhocko@kernel.org> writes:
>> 
>> > On Thu 02-04-20 15:03:23, Huang, Ying wrote:
> [...]
>> >> > Could you explain why do we need this WARN_ON? I haven't really checked
>> >> > the swap support for THP but cannot we have normal swap pmd entries?
>> >> 
>> >> I have some patches to add the swap pmd entry support, but they haven't
>> >> been merged yet.
>> >> 
>> >> Similar checks are for all THP migration code paths, so I follow the
>> >> same style.
>> >
>> > I haven't checked other migration code paths but what is the reason to
>> > add the warning here? Even if this shouldn't happen, smaps is perfectly
>> > fine to ignore that situation, no?
>> 
>> Yes. smaps itself is perfectly fine to ignore it.  I think this is used
>> to find bugs in other code paths such as THP migration related.
>
> Please do not add new warnings without a good an strong reasons. As a
> matter of fact there are people running with panic_on_warn and each
> warning is fatal for them. Please also note that this is a user trigable
> path and that requires even more care.

OK for me.

Best Regards,
Huang, Ying