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 7AC05CDC173 for ; Tue, 6 Jan 2026 12:03:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E2F046B00A3; Tue, 6 Jan 2026 07:03:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DFD146B00A4; Tue, 6 Jan 2026 07:03:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D29CD6B00A5; Tue, 6 Jan 2026 07:03:17 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id C59B86B00A3 for ; Tue, 6 Jan 2026 07:03:17 -0500 (EST) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 85A611B82D for ; Tue, 6 Jan 2026 12:03:17 +0000 (UTC) X-FDA: 84301403634.11.EF6982F Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) by imf29.hostedemail.com (Postfix) with ESMTP id D737C120017 for ; Tue, 6 Jan 2026 12:03:15 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kdzRBVLv; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.174 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767700996; a=rsa-sha256; cv=none; b=1iKy1QwfDc6W4HXVyTTM/HYWGuPOFqWdGll4ploL8xtMhu6Pulna62/2UPy2qKVktgvTiF up7fnn7ahuaVTuGOoxvrMkJR09nqRoPL3ZfhhzhyV0TpR746LzeO7aFokcgYwKC0lPWPKK rA+EKWjtk27+vFrplyFVTR6b5BRcu8I= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kdzRBVLv; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.174 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=1767700996; 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=a7ZSpmV1GOsNakyqG4Y6rXXXLNbQp9KgX3hJT5l75BA9SVmjEkiI37vp1bUjb7PBzJpxrZ CxAie8xV1bxdp2eyB17jY1uTLZMiNR4e4LXRox7oNNRJnLcjZJpHNJZNCixjaX3VPw516O ZQGB2LP3+oOMvVyWJu0e4n+VvJ+LKX4= 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=1767700993; 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=kdzRBVLvNh8jbNQ59PhwNwBz4pfvxAXmnXMGo9B2oaSAsbzuAsrs+BYB75BRamLHGE8OCb hf1s5SBgskmqMmdkwiWDDkI1Apoa/QMuMicJOLZ/aSx32ijPVk6KHcwfjBgGnwT8S86Amz iUAvdmGMLmr0DxBDKwYjPDSG+VmR+Y8= From: Lance Yang 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 RESEND v3 0/2] skip redundant TLB sync IPIs Date: Tue, 6 Jan 2026 20:03:01 +0800 Message-ID: <20260106120303.38124-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: D737C120017 X-Rspamd-Server: rspam10 X-Stat-Signature: xo34wo8pwpmpjdkrsu8p5ktnxw1sran7 X-HE-Tag: 1767700995-7843 X-HE-Meta: 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 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