On Wed, 6 Mar 2013, Ric Mason wrote: [ I've deleted the context because that was about the unstable tree, and here you have moved to asking about a case in the stable tree. ] > > For the case of a ksm page is migrated to a different NUMA node and migrate > its stable node to the right tree and collide with an existing stable node. > get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid) can capture nothing That's not so: as I've pointed out before, ksm_migrate_page() updates stable_node->kpfn for the new page on the new NUMA node; but it cannot (get the right locking to) move the stable_node to its new tree at that time. It's moved out once ksmd notices that it's in the wrong NUMA node tree - perhaps when one its rmap_items reaches the head of cmp_and_merge_page(), or perhaps here in stable_tree_search() when it matches another page coming in to cmp_and_merge_page(). You may be concentrating on the case when that "another page" is a ksm page migrated from a different NUMA node; and overlooking the case of when the matching ksm page in this stable tree has itself been migrated. > since stable_node is the node in the right stable tree, nothing happen to it > before this check. Did you intend to check get_kpfn_nid(page_node->kpfn) != > NUMA(page_node->nid) ? Certainly not: page_node is usually NULL. But I could have checked get_kpfn_nid(stable_node->kpfn) != nid: I was duplicating the test from cmp_and_merge_page(), but here we do have local variable nid. 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>