On Sat, 17 Apr 2010, Bob Liu wrote: > > GFP_THISNODE forces allocation from the node. Without it we will fallback. > > > > Yeah, but I think we shouldn't fallback at this case, what we want is > alloc a page > from exactly the dest node during migrate_to_node(dest).So I added > GFP_THISNODE. Why would we want that? > > And mel concerned that > ==== > This appears to be a valid bug fix. I agree that the way things are structured > that __GFP_THISNODE should be used in new_node_page(). But maybe a follow-on > patch is also required. The behaviour is now; > > o new_node_page will not return NULL if the target node is empty (fine). > o migrate_pages will translate this into -ENOMEM (fine) > o do_migrate_pages breaks early if it gets -ENOMEM ? > > It's the last part I'd like you to double check. migrate_pages() takes a > nodemask of allowed nodes to migrate to. Rather than sending this down > to the allocator, it iterates over the nodes allowed in the mask. If one > of those nodes is full, it returns -ENOMEM. > > If -ENOMEM is returned from migrate_pages, should it not move to the > next node? > ==== ?? It will move onto the next node if you leave things as is. If you add GFP_THISNODE then you can get NULL back from the page allocator because there is no memory on the local node. Without GFP_THISNODe the allocation will fallback. > In my opinion, when we want to preserve the relative position of the page to > the beginning of the node set, early return is ok. Else should try to alloc the > new page from the next node(to_nodes). ??? > So I added retry path to allocate new page from next node only when > from_nodes' weight is different from to_nodes', this case the user should > konw the relative position of the page to the beginning of the node set > can be changed. There is no point in your patch since the functionality is already there without it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>