Messages in this thread | | | Date | Thu, 22 Mar 2012 15:07:00 -0400 | From | Larry Woodman <> | Subject | Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node |
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On 03/22/2012 02:51 PM, Christoph Lameter wrote: > On Thu, 22 Mar 2012, KOSAKI Motohiro wrote: > >> CC to Christoph. >> >>> While moving tasks between cpusets I noticed some strange behavior. >>> Specifically if the nodes of the destination >>> cpuset are a subset of the nodes of the source cpuset do_migrate_pages() >>> will move pages that are already on a node >>> in the destination cpuset. The reason for this is do_migrate_pages() does >>> not check whether each node in the source >>> nodemask is in the destination nodemask before calling migrate_to_node(). If >>> we simply do this check and skip them >>> when the source is in the destination moving we wont move nodes that dont >>> need to be moved. >>> >>> Adding a little debug printk to migrate_to_node(): >>> >>> Without this change migrating tasks from a cpuset containing nodes 0-7 to a >>> cpuset containing nodes 3-4, we migrate >>> from ALL the nodes even if they are in the both the source and destination >>> nodesets: >>> >>> Migrating 7 to 4 >>> Migrating 6 to 3 >>> Migrating 5 to 4 >>> Migrating 4 to 3 >>> Migrating 1 to 4 >>> Migrating 3 to 4 >>> Migrating 0 to 3 >>> Migrating 2 to 3 >> Wait. >> >> This may be non-optimal for cpusets, but maybe optimal migrate_pages, >> especially >> the usecase is HPC. I guess this is intended behavior. I think we need to hear >> Christoph's intention. >> >> But, I'm not against this if he has no objection. > The use case for this is if you have an app running on nodes 3,4,5 on your > machine and now you want to shift it to 4,5,6. The expectation is that the > location of the pages relative to the first node stay the same. > Application may manage their locality given a range of nodes and each of > the x .. x+n nodes has their particular purpose. So to be clear on this, in that case the intention would be move 3 to 4, 4 to 5 and 5 to 6 to keep the node ordering the same?
Larry > If you justd copy 3 to 6 then the app may get confused when doing > additional allocations since different types of information is now stored > on the "first" node (which is now 4). > > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email:<a href=mailto:"dont@kvack.org"> email@kvack.org</a>
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