Re: [PATCH v4 4/7] x86/tlb: fall back to flush all when meet a THPlarge page

[Borislav Petkov]

On Thu, May 10, 2012 at 11:29:05AM +0200, Peter Zijlstra wrote:
> On Thu, 2012-05-10 at 13:00 +0800, Alex Shi wrote:
> > We don't need to flush large pages by PAGE_SIZE step, that just waste
> > time. and actually, large page don't need 'invlpg' optimizing according
> > to our macro benchmark. So, just flush whole TLB is enough for them.
> > 
> > The following result is tested on a 2CPU * 4cores * 2HT NHM EP machine,
> > with THP 'always' setting.
> 
> What does it do when you disable THP? That has_large_page() thing is a
> massive amount of pointer chasing..

Yeah, this looks like a bit of a overhead. Don't we have some per-mm
accounting of whether that mm struct has hugepages in mm/huge_memory.c,
i.e. something like what collapse_huge_page() does, for example, at the
end by incrementing khugepaged_pages_collapsed but in a per-mm variable?

And make this part of the THP code so we get it for free here.

Is Andrea on the CC list... hm, no, CCed.

Andrea?

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Boris.

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