From b5a210ad153e5448876c422f5c77d3dcd83abac6 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 19 Mar 2025 13:25:20 -0400 Subject: x86/mm: Only do broadcast flush from reclaim if pages were unmapped Track whether pages were unmapped from any MM (even ones with a currently empty mm_cpumask) by the reclaim code, to figure out whether or not broadcast TLB flush should be done when reclaim finishes. The reason any MM must be tracked, and not only ones contributing to the tlbbatch cpumask, is that broadcast ASIDs are expected to be kept up to date even on CPUs where the MM is not currently active. This change allows reclaim to avoid doing TLB flushes when only clean page cache pages and/or slab memory were reclaimed, which is fairly common. ( This is a simpler alternative to the code that was in my INVLPGB series before, and it seems to capture most of the benefit due to how common it is to reclaim only page cache. ) Signed-off-by: Rik van Riel Signed-off-by: Ingo Molnar Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250319132520.6b10ad90@fangorn --- arch/x86/include/asm/tlbbatch.h | 5 +++++ arch/x86/include/asm/tlbflush.h | 1 + arch/x86/mm/tlb.c | 3 ++- 3 files changed, 8 insertions(+), 1 deletion(-) --- a/arch/x86/include/asm/tlbbatch.h +++ b/arch/x86/include/asm/tlbbatch.h @@ -10,6 +10,11 @@ struct arch_tlbflush_unmap_batch { * the PFNs being flushed.. */ struct cpumask cpumask; + /* + * Set if pages were unmapped from any MM, even one that does not + * have active CPUs in its cpumask. + */ + bool unmapped_pages; }; #endif /* _ARCH_X86_TLBBATCH_H */ --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -353,6 +353,7 @@ static inline void arch_tlbbatch_add_pen { inc_mm_tlb_gen(mm); cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm)); + batch->unmapped_pages = true; mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL); } --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -1633,8 +1633,9 @@ void arch_tlbbatch_flush(struct arch_tlb * a local TLB flush is needed. Optimize this use-case by calling * flush_tlb_func_local() directly in this case. */ - if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) { + if (cpu_feature_enabled(X86_FEATURE_INVLPGB) && batch->unmapped_pages) { invlpgb_flush_all_nonglobals(); + batch->unmapped_pages = false; } else if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) { flush_tlb_multi(&batch->cpumask, info); } else if (cpumask_test_cpu(cpu, &batch->cpumask)) {