On Wed, 9 Feb 2022, Geert Uytterhoeven wrote: > On Wed, Feb 9, 2022 at 4:38 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > The thing is, SeongJae's patch makes me wonder, why did it not need a > > !CONFIG_MMU definition for need_mlock_page_drain() too? That's because > > mm/swap.c's call to it is under an #ifdef CONFIG_SMP, and I imagine that > > CONFIG_MMU=n usually goes along with (but does not necessarily imply?) > > CONFIG_SMP=n. It'll be safer to add a need_mlock_page_drain() stub too. > > RISC-V K210 is SMP without MMU. Thanks Geert, that makes it very clear that we also want the stub for need_mlock_page_drain(). I'll follow now with update of SeongJae's patch. My fear of wider implications of not having CONFIG_SMP turned out to be a false alarm. The UP lru_add_drain_cpu() calls mlock_page_drain() just like the SMP one does: the difference between them is merely that the UP case doesn't need an efficient way for asking in advance whether drain on another cpu will be needed. Hugh
