* Dave Hansen <dave.hansen@xxxxxxxxx> 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 <dave.hansen@xxxxxxxxxxxxxxx> 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
