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 <dave.hansen@xxxxxxxxxxxxxxx>
