On Thu, Dec 26, 2024 at 09:35:32AM +0800, Huang, Ying wrote: > > Having two files for each node (nodeN, defaultN) seems a bit too > > cluttered for the user perspective. Making the nodeN interfaces serve > > multiple purposes (i.e. echo -1 into the nodes will output the default > > value for that node) also seems a bit too complicated as well, in my > > opinion. Maybe having a file 'weight_tables' that contains a table of > > default/user/effective weights (as have been used in these conversations) > > might be useful for the user? (Or maybe just the defaults) > > > > Then a workflow for the user may be as such: > > > > $ cat /sys/kernel/mm/mempolicy/weighted_interleave/weight_tables > > default vales: [4,7,2] > > user values: [-,-,-] > > effective: [4,7,2] > > AFAIK, this breaks the sysfs attribute format rule as follows. > > https://docs.kernel.org/filesystems/sysfs.html#attributes > > It's hard to use array sysfs attribute here too. Because the node ID > may be non-consecutive. This makes it hard to read. > Would generally agree. I think essentially a use_defaults => (0 | 1) interface is probably the best we can do. Setting any node changes use_defaults from 1 => 0 echoing 1 into use_default clears user_values This still allows 0 to be a manual "reset specific node to default" mechanism for a specific node, and gives us a clean override. The only question is a matter of hotplug behavior nodes_online: 0,1 default_values: [5,3] user_values : [-,-] event: node1 is taken offline default_values: [5,3] <-- nothing happens event: node1 comes back online with different bandwidth attribute default_values: [6,5] <-- reweight as occured silently event: user sets a custom value (node1 <= 2) default_values: [6,5] user_values: [6,2] <= note, *no reduction* event: node1 is taken offline default_values: [6,5] user_values: [6,2] <= value still present but not used event: node1 comes back online with different bandwidth attribute default_values: [5,3] <-- default reweight has occurred silently user_values : [6,2] <-- user responsible for triggering re-weight The user has the option of echo 1 > /sys/.../weghted_interleave/user_defaults result default_values: [5,3] user_values : [-,-] or echo 0 > /sys/.../weighted_interleave/node1 result default_values: [5,3] user_values : [6,3] <= only node1 is updated, no re-weight Basically, if the user ever sets any value, we never automatically pull new values in, and the admin is responsible for triggering a re-weight (use_default) or manually reweighting *all* nodes - because changing values implies a change in the bandwidth distribution anyway. I think this makes the most sense. ~Gregory
