Re: [PATCH v7 3/6] mm: Introduce VM_LOCKONFAULT

On Thu, 20 Aug 2015, Michal Hocko wrote:

On Wed 19-08-15 17:33:45, Eric B Munson wrote:
[...]

quoted

The group which asked for this feature here
wants the ability to distinguish between LOCKED and LOCKONFAULT regions
and without the VMA flag there isn't a way to do that.

Could you be more specific on why this is needed?

They want to keep metrics on the amount of memory used in a LOCKONFAULT
region versus the address space of the region.

quoted

Do we know that these last two open flags are needed right now or is
this speculation that they will be and that none of the other VMA flags
can be reclaimed?

I do not think they are needed by anybody right now but that is not a
reason why it should be used without a really strong justification.
If the discoverability is really needed then fair enough but I haven't
seen any justification for that yet.

To be completely clear you believe that if the metrics collection is
not a strong enough justification, it is better to expand the mm_struct
by another unsigned long than to use one of these bits right?