On Sat, 26 Jan 2013, Simon Jeons wrote: > On Fri, 2013-01-25 at 17:54 -0800, Hugh Dickins wrote: > > From: Petr Holasek <pholasek@xxxxxxxxxx> > > @@ -1122,6 +1166,18 @@ struct rmap_item *unstable_tree_search_i > > return NULL; > > } > > > > + /* > > + * If tree_page has been migrated to another NUMA node, it > > + * will be flushed out and put into the right unstable tree > > Then why not insert the new page to unstable tree during page migration > against current upstream? Because default behavior is merge across > nodes. I don't understand the words "against current upstream" in your question. We cannot move a page (strictly, a node) from one tree to another during page migration itself, because the necessary ksm_thread_mutex is not held. Not would we even want to while "merge across nodes". Ah, perhaps you are pointing out that in current upstream, the only user of ksm page migration is memory hotremove, which in current upstream does hold ksm_thread_mutex. So you'd like us to add code for moving a node from one tree to another in ksm_migrate_page() (and what would it do when it collides with an existing node?), code which will then be removed a few patches later when ksm page migration is fully enabled? No, I'm not going to put any more thought into that. When Andrea pointed out the problem with Petr's original change to ksm_migrate_page(), I did indeed think that we could do something cleverer at that point; but once I got down to trying it, found that a dead end. I wasn't going to be able to test the hotremove case properly anyway, so no good pursuing solutions that couldn't be generalized. Hugh -- 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>