Gregory Price <gregory.price@xxxxxxxxxxxx> writes: > On Wed, Jan 03, 2024 at 10:45:53AM +0800, Huang, Ying wrote: >> >> > The minimum functionality is everything receiving a default weight of 1, >> > such that weighted interleave's behavior defaults to round-robin >> > interleave. This gets the system off the ground. >> >> I don't think that we need to implement all functionalities now. But, >> we may need to consider more especially if it may impact the user space >> interface. The default base weight is something like that. If we >> change the default base weight from "1" to "16" later, users may be >> surprised. So, I think it's better to discuss it now. >> > > This is a hill I don't particularly care to die on. I think the weights > are likely to end up being set at boot and rebalanced as (rare) hotplug > events occur. > > So if people think the default weight should be 3,16,24 or 123, i don't > think it's going to matter. > >> >> We can use a wrapper function to hide the logic. >> > > Done. I'll push a new set tomorrow. > >> > I think it also allows MPOL_F_GWEIGHT to be eliminated. >> >> Do we need a way to distinguish whether to copy the global weights to >> local weights when the memory policy is created? That is, when the >> global weights are changed later, will the changes be used? One >> possible solution is >> >> - If no weights are specified in set_mempolicy2(), the global weights >> will be used always. >> >> - If at least one weight is specified in set_mempolicy2(), it will be >> used, and the other weights in global weights will be copied to the >> local weights. That is, changes to the global weights will not be >> used. >> > > What's confusing about that is that if a user sets a weight to 0, > they'll get a non-0 weight - always. > > In my opinion, if we want to make '0' mean 'use system default', then > it should mean 'ALWAYS use system default for this node'. > > "Use the system default at the time the syscall was called, and do not > update to use a new system default if that default is changed" is > confusing. > > If you say use a global value, use the global value. Simple. I mainly have concerns about consistency. The global weights can be changed while the local weights are fixed. For example, - Weights of node 0,1 is [3, 1] initially - Process A call set_mempolicy2() to set weights to [4, 0], that is, use default weight for node 1. - After hotplug, the weights of node is changed to [12, 4, 1], now the effective weights used in process A becomes [4, 4]. Which is hardly desired. Another choice is to disallow "0" as weight in set_mempolicy2(). -- Best Regards, Huang, Ying
