On 12/13/20 10:53 PM, Nicholas Piggin wrote: > diff --git a/arch/Kconfig b/arch/Kconfig > index 84faaba66364..e69c974369cc 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -443,9 +443,22 @@ config MMU_LAZY_TLB > config MMU_LAZY_TLB_REFCOUNT > def_bool y > depends on MMU_LAZY_TLB > + depends on !MMU_LAZY_TLB_SHOOTDOWN > help > - This must be enabled if MMU_LAZY_TLB is enabled until the next > - patch. > + This refcounts the mm that is used as the lazy TLB mm when switching > + switching to a kernel thread. duplicate "switching". > + > +config MMU_LAZY_TLB_SHOOTDOWN > + bool > + depends on MMU_LAZY_TLB > + help > + Instead of refcounting the "lazy tlb" mm struct, which can cause > + contention with multi-threaded apps on large multiprocessor systems, > + this option causes __mmdrop to IPI all CPUs in the mm_cpumask and > + switch to init_mm if they were using the to-be-freed mm as the lazy > + tlb. To implement this, architectures must use _lazy_tlb variants of > + mm refcounting, and mm_cpumask must include at least all possible > + CPUs in which mm might be lazy. > > config ARCH_HAVE_NMI_SAFE_CMPXCHG > bool --
