* Dave Hansen wrote:
> On 9/13/19 2:54 AM, Kirill A. Shutemov wrote:
> > The next major release of distributions expected to have
> > CONFIG_X86_5LEVEL=y.
>
> It's probably worth noting that this exposes to two kinds of possible
> performance issues:
>
> First is the overhead of having the 5-level code on 4-level hardware.
> We haven't seen any regressions there in quite a while. Kirill talked
> about this in the changelog.
>
> Second is the overhead of having 5-level paging active on 5-level
> hardware versus using 4-level paging on hardware *capable* of 5-level.
> That is, of course, much harder to measure since 5-level hardware is not
> publicly available. But, we've tested this quite a bit and we're pretty
> confident that it will not cause regressions, especially on systems
> where apps don't opt in to the larger address space.
>
> I do think endeavoring to have mainline's defaults match the most common
> distro configs is a good idea, and now is as good of a time as any.
>
> Acked-by: Dave Hansen
Ok - in terms of timing it's obviously *way* too late for v5.4, so I've
queued it up for the v5.5 merge window in tip:x86/mm. This should give it
2-3 months of additional testing to shake out any weird interactions and
quirks.
Thanks,
Ingo
