Gregory Price <gourry@xxxxxxxxxx> writes: > 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 difficulty is that users don't know the default value when they reset a node's weight. We don't have an interface to show them. So, I suggest to disable the functionality: "reset specific node to default". They can still use "echo 1 > use_defaults" to reset all nodes to default. > 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. --- Best Regards, Huang, Ying
