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Howlett wrote: >> * David Hildenbrand [250515 13:30]: >>>>> >>>> >>>> Did we document all this? :) >>>> >>>> It'd be good to be super explicit about these sorts of 'dependency c= hains'. >>>> >>> >>> Documentation/admin-guide/mm/transhuge.rst has under "Global THP cont= rols" >>> quite some stuff about all that, yes. >>> >>> The whole document needs an overhaul, to clarify on the whole termino= logy, >>> make it consistent, and better explain how the pagecache behaves etc.= On my >>> todo list, but I'm afraid it will be a bit of work to get it right / = please >>> most people. >> >> Yes, the whole thing is making me grumpy (more than my default state).= >> The more I think about it, the more I don't like the prctl approach >> either... > > prctl() feels like it's literally never, ever the right choice. > > It feels like we shove all the dark stuff we want to put under the rug > there. > > Reading the man page is genuinely frightening. there's stuff about VMAs= _I > wasn't aware of_. > > It's also never really the _right time_ to do it - it's not process > inception is it? It's when the process has started, now you suddenly fi= ddle > with it. > > Then relying on mm flags being propagated over fork/exec is just, it's = a > hack really. > >> >> I more than dislike flags2... I hate it. > > Yeah, to be clear - I will NACK any series that tries to add flags2 unl= ess > a VERY VERY good justification is given. It's horrid. And frankly this > feature doesn't warrant something as horrible. > > But making mm->flags 64-bit on 32-bit kernels (which are in effect > deprecated in my view) would fix this. > >> >> but no prctl, no cgroups, no bpf.. what is left? A new policy groups >> thing? No, not that either, please. BPF might be OK, as long as we provide right functions for BPF to manipul= ate system, process, MM, VMA level knobs. My only objection to Yafang's patch= [1] is that the patch adds a VMA parameter to the global hugepage checking funct= ions. My take on BPF approach is that it does not add new APIs, so we can chang= e it at any time, assuming people is willing to accept that the functions inst= rumented by BPF can go away at any time and the corresponding BPF programs will no= t work forever. It allows us to explore various huge page policies without the b= urden of maintaining APIs. Eventually, huge page policies become transparent af= ter we learn enough. [1] https://lore.kernel.org/linux-mm/20250429024139.34365-1-laoar.shao@gm= ail.com/ -- Best Regards, Yan, Zi