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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? The dual question of when huge pages make sense, is when they don't make sense. In current proposal of Adhemerval he is really focusing on the dual question, and identifying a specific case where they do not make sense. IMO, huge pages make sense for the stack every time the programmer or the user of the system so thinks and profiles as a benefit. It really depends on the use case. If stack allocation is big enough to make use of huge pages, it is definetely a benefit to use them to reduce TLB pressure. Regarding precisely identifying when hugepages are benefitial this is really an unpredictable case by case problem and for that matter hard to predict. I don't think you can easily find an heuristic that will solve the properly detect that. Cheers, Cupertino > > Cheers, > Wilco