On Mon, 9 Dec 2013, Mel Gorman wrote: > I looked at what would be required to implement migration entry support for > PMDs. It's major surgery because we do not have something like swap-like > entries to use at that page table level. It looked like it would require > inserting a fake entry (easiest would be to point to a global page) that > all page table walkers would recognise, blocking on it and teaching every > page table walker to get it right. Well something needs to cause a fault and stop accesses to the page. > One can't do something simple like clear the entry out because then the > no page handlers for GUP or faults insert the zero page behind and it goes > to hell and we can't hold the page table lock across the migration copy. Right you need to have special migration entry there. Same as for regular sized pages. > The patch flushes the TLBs as it is and future accesses are help up in the > NUMA hinting fault handler. It's functionally similar to having a migration > entry albeit it is special cased to handle just automatic NUMA balancing Hmmm... Hopefully that will work. I'd rather see a clean extension of what we use for regular pages. If we add functionality to huge pages to operate more like regular ones then this could be an issue. -- 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>