Re: [PATCH v3 4/4] arm64: support batched/deferred tlb shootdown during page reclamation
From: Anshuman Khandual <hidden>
Date: 2022-09-20 08:46:18
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On 9/20/22 09:09, Barry Song wrote:
On Tue, Sep 20, 2022 at 3:00 PM Anshuman Khandual [off-list ref] wrote:quoted
On 8/22/22 13:51, Yicong Yang wrote:quoted
+static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) +{ + return true; +}This needs to be conditional on systems, where there will be performance improvements, and should not just be enabled all the time on all systems. num_online_cpus() > X, which does not hold any cpu hotplug lock would be a good metric ?for a small system, i don't see how this patch will help, e.g. cpus <= 4; so we can actually disable tlb-batch on small systems.
Do not subscribe ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH based on NR_CPUS ? That might not help much as the default value is 256 for NR_CPUS. OR arch_tlbbatch_should_defer() checks on 1. online cpus (dont enable batched TLB if <= X) 2. ARM64_WORKAROUND_REPEAT_TLBI (dont enable batched TLB)
just need to check if we will have any race condition since hotplug will make the condition true and false dynamically.
If should_defer_flush() evaluate to be false, then ptep_clear_flush() clears and flushes the entry right away. This should not race with other queued up TLBI requests, which will be flushed separately. Wondering how there can be a race here ! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel