On Mon, Dec 03, 2012 at 10:52:27AM +0800, Lin Feng wrote: > > > On 11/30/2012 07:00 PM, Mel Gorman wrote: > >> > >> Well, that's a fairly low-level implementation detail. A more typical > >> approach would be to add a new get_user_pages_non_movable() or such. > >> That would probably have the same signature as get_user_pages(), with > >> one additional argument. Then get_user_pages() becomes a one-line > >> wrapper which passes in a particular value of that argument. > >> > > > > That is going in the direction that all pinned pages become MIGRATE_UNMOVABLE > > allocations. That will impact THP availability by increasing the number > > of MIGRATE_UNMOVABLE blocks that exist and it would hit every user -- > > not just those that care about ZONE_MOVABLE. > > > > I'm likely to NAK such a patch if it's only about node hot-remove because > > it's much more of a corner case than wanting to use THP. > > > > I would prefer if get_user_pages() checked if the page it was about to > > pin was in ZONE_MOVABLE and if so, migrate it at that point before it's > > pinned. It'll be expensive but will guarantee ZONE_MOVABLE availability > > if that's what they want. The CMA people might also want to take > > advantage of this if the page happened to be in the MIGRATE_CMA > > pageblock. > > > hi Mel, > > Thanks for your suggestion. > My initial idea is also to restrict the impact as little as possible so > migrate such pages as we need. > But even to such "going to pin pages", most of them are going to be released > soon, so deal with them all in the same way is really *expensive*. > Then you need to somehow distinguish between short-lived pins and long-lived pins and only migrate the long-lived pins. I didn't research how this could be implemented -- Mel Gorman 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>