On Thu 20-08-15 13:03:09, Eric B Munson wrote: > On Thu, 20 Aug 2015, Michal Hocko wrote: > > > On Wed 19-08-15 17:33:45, Eric B Munson wrote: > > [...] > > > 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. /proc/<pid>/smaps already exports that information AFAICS. It exports VMA flags including VM_LOCKED and if rss < size then this is clearly LOCKONFAULT because the standard mlock semantic is to populate. Would that be sufficient? Now, it is true that LOCKONFAULT wouldn't be distinguishable from MAP_LOCKED which failed to populate but does that really matter? It is LOCKONFAULT in a way as well. > > > 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? A simple bool is sufficient for that. And yes I think we should go with per mm_struct flag rather than the additional vma flag if it has only the global (whole address space) scope - which would be the case if the LOCKONFAULT is always an mlock modifier and the persistance is needed only for MCL_FUTURE. Which is imho a sane semantic. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>