On Sat, Dec 21, 2024 at 01:57:58PM +0800, Huang, Ying wrote: > Hi, Joshua, > > Joshua Hahn <joshua.hahnjy@xxxxxxxxx> writes: > > > On Fri, 13 Dec 2024 15:19:20 +0900 Hyeonggon Yoo <hyeonggon.yoo@xxxxxx> wrote: > > > >> On 2024-12-11 06:54 AM, Joshua Hahn wrote: > > [snip] > > > > > [-----8<-----] > > > >> > +What: /sys/kernel/mm/mempolicy/weighted_interleave/max_node_weight > > I don't think that we need a new knob for this. Just use a reasonable > default value, for example, 32 or 16. If it turns out that a knob will > be really helpful, we can add it at that time. For now, I don't think > the requirements are clear. And, this is a new ABI and we need to > maintain it almost for ever. We must be careful about new knob. > This is fair. We spent a good amount of time modeling the best effective maximum weight and basically came to the conclusion that 32 has a good balance of minimizing error and being somewhat aggressive. Ripping out the sysfs is easy enough. > > > > Regardless of what implementation makes sense, I can re-write the > > description so that there is no ambiguity when it comes to the > > expected behavior of the code. Thank you for pointing this out! > > I don't think that it's a good idea to override the user supplied > configuration values. User configurations always have higher priority > than system default configurations. IIUC, this is the general rule of > Linux kernel user space interface. > We discussed this and decided it was confusing no matter what we did. If new data comes in (CDAT data from a hotplug event), then the weights are now wrong for the new global state - regardless of whether the user set a weight manually or not. This also allowed us to simplify the implementation a bit. But if generally we need to preserve user settings, then I think the best we can do to provide a sane system is ignore the user setting when re-weighting on a hotplug event. e.g. user has not set a value default_values [5,2,-] <- 1 node not set, expected to be hotplugged user_values [-,-,-] <- user has not set values effective [5,2,-] hotplug event default_values [2,1,1] - reweight has occurred user_values [-,-,-] effective [2,1,1] e.g. user has set a value default_values [5,2,-] <- 1 node not set, expected to be hotplugged user_values [4,-,-] <- user has only set one value effective [4,2,-] hotplug event default_values [2,1,1] - reweight has occurred user_values [4,-,-] effective [4,1,1] So default values get updated, but user values get left alone. If that's sane we'll fix it up. > --- > Best Regards, > Huang, Ying
