Re: [PATCH] nptl: Disable THP on thread stack if it incurs in large RSS usage

[Wilco Dijkstra via Libc-alpha <libc-alpha@sourceware.org>]

Hi Adhemerval,

>> The question is, under what circumstances are huge pages in stacks beneficial and
>> in which cases are they not? If have a good answer to that, then we can automatically
>> do the right thing without needing a tuning.
>> 
> 
> Afaiu the issue is not whether huge page in stacks is beneficial, but rather 
> when kernel will fall back to default pages anyway which will be just waste 
> cycles.  Another option would be tune the default stack and guard size
> to avoid this issue, but this might require some more heuristics to find a 
> good spot to avoid too much VMA waste.

The kernel won't fallback to standard pages - like I said, it really allocates a huge
page when it can (based on alignment of the stack) and that is what causes the
increase of RSS size. But that's not evidence of an issue.

So the real question is when do huge pages make sense for stacks?

Cheers,
Wilco