Messages in this thread | | | Date | Wed, 06 Mar 2013 14:58:36 +0800 | From | Ric Mason <> | Subject | Re: [PATCH 2/7] ksm: treat unstable nid like in stable tree |
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Hi Hugh, On 03/06/2013 01:05 PM, Hugh Dickins wrote: > 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
Are you sure? list_del(&page_node->list) and DO_NUMA(page_node->nid = nid) will trigger panic now. > 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
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