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SubjectRe: [PATCH v2 3/5] lazy tlb: shoot lazies, a non-refcounting lazy tlb option
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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


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