From 0b7eb55cb706e92d6073e4ab63ccd4d219cf2cda Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 19 Mar 2025 13:25:20 -0400 Subject: [PATCH] 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(-) diff --git a/arch/x86/include/asm/tlbbatch.h b/arch/x86/include/asm/tlbbatch.h index 1ad56eb3e8a8f..80aaf64ff25f4 100644 --- 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 */ diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 7cad283d502d0..a9af8759de347 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -353,6 +353,7 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b { 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); } diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 0efd99053c09d..0925768d00cb5 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -1633,8 +1633,9 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) * 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)) {