@ljs this is an image (though it is years out of date) of the main heap of some Chrome process: https://drive.google.com/file/d/1rI3mFhKzvE9L8C0szPJBJeuN-lq9XdYC/view
Every line is 2MiB of virtual address space, and the barely visible dark stuff on the left and right is non-present PROT_NONE stuff
@ljs maybe Chrome is one of the applications that will get the biggest performance boost from that 
because almost all their VMAs are smaller than 2M for guard page reasons, and they also happen to use 16K as some kinda allocation block size in their allocator
@ljs yeah I enabled 16K mTHP on my chonky AMD home PC
establishing higher order folios will have fault scalability/reclaim advantages also
By the time khugepaged comes around, fault scalability is probably not much of a concern anymore, right? Since you're probably done faulting when khugepaged comes around to collapse stuff? Unless we're talking about swapin performance. But yeah, reclaim I could see.
As for follow up, I think you could at least in theory benefit from multiple mTHP sizes as if we were unable to obtain a larger mTHP size we could try for smaller, but you'd always want to have the largest possible.
I think you wouldn't get a benefit out of it in terms of TLB - like, on modern AMD machines, I believe if you can't get a 16K page, then the TLB will have to use 4K entries anyway and from the TLB perspective, there's no sense in having 8K pages?
@ljs I mean, it's pretty clear to be that it would improve TLB stuff, my question is: Does it only improve TLB stuff, or is there something else it also improves?
(And the follow-up question would be: Do people actually expect to want a bunch of different mTHP sizes or is the expected usecase to have a single anon mTHP size?)
so what is the reason why people want anon mTHP khugepaged? is that only for TLB reasons (which means they really just want one more hugepage size between 4K and 2M) or is there something more going on where this is supposed to improve internal kernel efficiency of vmscan or something like that?