On Fri, 26 Feb 2021 11:48:18 +0800 Jacob Wen <jian.w.wen@xxxxxxxxxx> wrote: > Removing a kernel module to see if it releases a lot of memory is > helpful to quickly find out the root causes of some issues. > > It seems nice to reserve the symbols. I don't have a relevant use case > so it's just my 2 cents. It's much more complex than that. We do something similar, where we keep the kallsyms for the module init code (otherwise when tracing a module that is loaded, you wont be able to see its functions). But the complexity comes from the fact that kallsyms has addresses associated to functions that no longer exist. Now what happens when new code maps at those addresses? It confuses kallsyms. Yeah, unloading of a module will turn function names into their original address, and worse, can even show function names for new code added. But there's not much we can do without having to save all kallsyms that were ever loaded, along with time stamps to know when they were valid. And remember, this is all in kernel memory that is never swapped out. If you want to add a feature to do something like that go ahead. I would recommend a "time out" where after a given time (user defined) that older symbols are flushed from the system, and perhaps even allow the user to define the number of symbols to keep around after they are gone. At least this will let the users decide how much memory they want to waste for this. -- Steve
