From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B4BBACDC166 for ; Tue, 6 Jan 2026 11:51:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 52D1E6B009E; Tue, 6 Jan 2026 06:51:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 423386B009F; Tue, 6 Jan 2026 06:51:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2BE836B00A0; Tue, 6 Jan 2026 06:51:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 140966B009E for ; Tue, 6 Jan 2026 06:51:31 -0500 (EST) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id A8E098BF60 for ; Tue, 6 Jan 2026 11:51:30 +0000 (UTC) X-FDA: 84301373940.11.2AB2D2C Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) by imf03.hostedemail.com (Postfix) with ESMTP id D95A62000A for ; Tue, 6 Jan 2026 11:51:28 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=e1LM69EH; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf03.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767700289; a=rsa-sha256; cv=none; b=lhdq7UXrRD1IMm41gswosR4tC3aIJ9Bfk+G2b4AbQMnASVJQoB7k1m49qRb5LAnkl4IpH+ u4ums/2oNpIB+FgfBEpECRSnGIRgen9wfrSsey+cJDyuuIxvT2zDnjcK8CioayJn2oYqym 3jJkz+Ii0UurWLOZJRGXD//Qkr9FeJ8= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=e1LM69EH; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf03.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767700289; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=iklw0RInONOSh+e9xelR5uEAOvlruMIvuc7amxeOT2I=; b=a/J1AYhWhAA+GtpZLg4BLRoh1aTVa2wcDQc7SD/OU7Lsp/Kjk1O/WcQ2uR1/YZDCO+cv8I uVMkU7v0thTQmS0ebS+9tTooIu/GG/4gpTBVutPJBavXtuLkXa75R+xNhubRrGYg8H5WT8 RRRko7c9t77A/C/ahwLBFviBNp0/M1o= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1767700286; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=iklw0RInONOSh+e9xelR5uEAOvlruMIvuc7amxeOT2I=; b=e1LM69EHdQpzC3zUSFx18F7ADHBf3b1Hls/i3QoR1He+c2eOrmtGPTw7XCnpLwoyBEEjZ2 T2OebBCEnpsLQemldztcr1Af3povcEeNa03S8f/agpusP1CwenaOpdY5ODQzmvCFvjIkm5 pzp5LKhTFWROjxnbIIWVIXpmQInyeJk= From: lance.yang@linux.dev To: akpm@linux-foundation.org Cc: david@kernel.org, dave.hansen@intel.com, dave.hansen@linux.intel.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shy828301@gmail.com, riel@surriel.com, jannh@google.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com Subject: [PATCH v3 0/2] skip redundant TLB sync IPIs Date: Tue, 6 Jan 2026 19:50:51 +0800 Message-ID: <20260106115053.32328-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D95A62000A X-Stat-Signature: a5ft549aajj6xgrw1u6t6chmc7wpmog4 X-Rspam-User: X-HE-Tag: 1767700288-59035 X-HE-Meta: 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 OQmPCEAh AHhvPrRIOq1d8pioOxpswzNQakkCTSq/J6BeblGGhBwgbX9b4g30HN+/ATljB3OgNHxO9L1SrDEUC4whLZ3uxPa//I9WYkUisFq97B1GcDXLOPt2zSvl6Sdu9WWbN+V26/0bavzWlcibLgRloch5hzOtSKz/UDoTHdk+l7doO0pvJ2tC4/8h5DRIIW+nG63ciRKmlALmHl3XJlyjsWSj3Y8cZimBF26Z1Rr2YFgcAZmsjNlNrechkgWDpCA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi all, When unsharing hugetlb PMD page tables or collapsing pages in khugepaged, we send two IPIs: one for TLB invalidation, and another to synchronize with concurrent GUP-fast walkers. However, if the TLB flush already reaches all CPUs, the second IPI is redundant. GUP-fast runs with IRQs disabled, so when the TLB flush IPI completes, any concurrent GUP-fast must have finished. We now track whether IPIs were actually sent during TLB flush. We pass the mmu_gather context through the flush path, and native_flush_tlb_multi() sets a flag when sending IPIs. Works with PV and INVLPGB since only native_flush_tlb_multi() sets the flag - no matter what replaces pv_ops.mmu.flush_tlb_multi or whether INVLPGB is available. David Hildenbrand did the initial implementation. I built on his work and relied on off-list discussions to push it further - thanks a lot David! v2 -> v3: - Complete rewrite: use dynamic IPI tracking instead of static checks (per Dave Hansen, thanks!) - Track IPIs via mmu_gather: native_flush_tlb_multi() sets flag when actually sending IPIs - Motivation for skipping redundant IPIs explained by David: https://lore.kernel.org/linux-mm/1b27a3fa-359a-43d0-bdeb-c31341749367@kernel.org/ - https://lore.kernel.org/linux-mm/20251229145245.85452-1-lance.yang@linux.dev/ v1 -> v2: - Fix cover letter encoding to resolve send-email issues. Apologies for any email flood caused by the failed send attempts :( RFC -> v1: - Use a callback function in pv_mmu_ops instead of comparing function pointers (per David) - Embed the check directly in tlb_remove_table_sync_one() instead of requiring every caller to check explicitly (per David) - Move tlb_table_flush_implies_ipi_broadcast() outside of CONFIG_MMU_GATHER_RCU_TABLE_FREE to fix build error on architectures that don't enable this config. https://lore.kernel.org/oe-kbuild-all/202512142156.cShiu6PU-lkp@intel.com/ - https://lore.kernel.org/linux-mm/20251213080038.10917-1-lance.yang@linux.dev/ Lance Yang (2): mm/tlb: skip redundant IPI when TLB flush already synchronized mm: introduce pmdp_collapse_flush_sync() to skip redundant IPI arch/x86/include/asm/tlb.h | 3 ++- arch/x86/include/asm/tlbflush.h | 9 +++++---- arch/x86/kernel/alternative.c | 2 +- arch/x86/kernel/ldt.c | 2 +- arch/x86/mm/tlb.c | 22 +++++++++++++++------ include/asm-generic/tlb.h | 14 +++++++++----- include/linux/pgtable.h | 13 +++++++++---- mm/khugepaged.c | 9 +++------ mm/mmu_gather.c | 26 ++++++++++++++++++------- mm/pgtable-generic.c | 34 +++++++++++++++++++++++++++++++++ 10 files changed, 99 insertions(+), 35 deletions(-) -- 2.49.0