742f3c8193
When UML handles a fork the page tables need to be brought up to date. That was done using brute force - full tlb flush. This is actually unnecessary, because the mapped-in mappings are all correct and the only mappings which need to be updated after a flush are any unmaps (so that paging works) as well as any pending protection changes. This optimization squeezes out up to 3% from a full kernel rebuild time under memory pressure. Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com> Signed-off-by: Richard Weinberger <richard@nod.at>