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 E8B83ECD983 for ; Thu, 5 Feb 2026 15:32:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 083716B0089; Thu, 5 Feb 2026 10:32:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 030D66B008A; Thu, 5 Feb 2026 10:32:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E751C6B0092; Thu, 5 Feb 2026 10:32:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id D74436B0089 for ; Thu, 5 Feb 2026 10:32:22 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 2782CC213B for ; Thu, 5 Feb 2026 15:32:22 +0000 (UTC) X-FDA: 84410794524.14.E37DB5A Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) by imf28.hostedemail.com (Postfix) with ESMTP id DB5EAC0014 for ; Thu, 5 Feb 2026 15:32:18 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=J4kMAUbZ; spf=pass (imf28.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.173 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770305539; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=nZCCu/D+A8/vQSICPy1kzHkrFU4nx4XMWizPhQHWKZE=; b=B5tpvr7q1MKBjJRm2X05vgKMts0ztCyFrCA6m2+/hvORDZw9yURLC1ydepKXEFv0LY9+/p x07P0KUARj769KEG6R6psdv6z8rEzRg/s3PcudzOwFlQx9JG4IAHBgr2XvSLjPP7CrWLGT zTfshZ5gzGujDYhwLic9eOP/7RS0dMs= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=J4kMAUbZ; spf=pass (imf28.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.173 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770305539; a=rsa-sha256; cv=none; b=eE9azTtBWNfFtww3k1xGTX6cxaVokiaQ247+v81KSOhsSQ1RbwxwvvF2AEEXOLfgOatulS CGCToYKIcWVDa9gYi4naGWsJ9ISWT/YRgLFG+YPw8gbIDd98cJDuV/58nlF0kW+sBbxj69 n6j2tf9iOI8qY80o3dlTvNAKdvUzlN0= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770305536; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nZCCu/D+A8/vQSICPy1kzHkrFU4nx4XMWizPhQHWKZE=; b=J4kMAUbZImqUoYGXnypA7JnwOQ6nbWXYNper/s+Ly1cCPQ7RG+AMBp08vyVNz/jHVoomLH peW91wvsv7DEEEi+N86L66kXjHcz1UF+GeftNiAXSBKVuphiyV+y27NFganbyWwBX5e5Xy 01KUQfoTLHkARKXBEAIocUoDnlGa78k= Date: Thu, 5 Feb 2026 23:31:48 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table Content-Language: en-US To: Dave Hansen , "David Hildenbrand (Arm)" , Peter Zijlstra Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, aneesh.kumar@kernel.org, arnd@arndb.de, baohua@kernel.org, baolin.wang@linux.alibaba.com, boris.ostrovsky@oracle.com, bp@alien8.de, dave.hansen@linux.intel.com, dev.jain@arm.com, hpa@zytor.com, hughd@google.com, ioworker0@gmail.com, jannh@google.com, jgross@suse.com, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mingo@redhat.com, npache@redhat.com, npiggin@gmail.com, pbonzini@redhat.com, riel@surriel.com, ryan.roberts@arm.com, seanjc@google.com, shy828301@gmail.com, tglx@linutronix.de, virtualization@lists.linux.dev, will@kernel.org, x86@kernel.org, ypodemsk@redhat.com, ziy@nvidia.com References: <20260202095414.GE2995752@noisy.programming.kicks-ass.net> <20260202110329.74397-1-lance.yang@linux.dev> <20260202125030.GB1395266@noisy.programming.kicks-ass.net> <4700e7ba-8456-4a93-9e28-7e5a3ca2a1be@linux.dev> <20260202133713.GF1395266@noisy.programming.kicks-ass.net> <540adec9-c483-460a-a682-f2076cf015c2@linux.dev> <20260202150957.GD1282955@noisy.programming.kicks-ass.net> <06d48a52-e4ec-47cd-b3fb-0fccd4dc49f4@kernel.org> <3026ad8d-92ad-4683-8c3e-733d4070d033@linux.dev> <64f3a75a-30ff-4bee-833c-be5dba05f72b@intel.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <64f3a75a-30ff-4bee-833c-be5dba05f72b@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Stat-Signature: tuwi64xsmqc8apx5h3gae7sceg8ygcdu X-Rspam-User: X-Rspamd-Queue-Id: DB5EAC0014 X-HE-Tag: 1770305538-381677 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: On 2026/2/5 23:09, Dave Hansen wrote: > On 2/5/26 07:01, Lance Yang wrote: >> So for now, neither approach looks good: tracking on the read side adss >> cost to GUP-fast, and syncing on the write side e.g. synchronize_rcu() >> is too slow on large systems. > > Which of the writers truly *need* synchronize_rcu()? > > What are they doing with the memory that they can't move forward unless > it's quiescent *now*? Without IPIs or synchronize_rcu(), IIUC, we have no way to know if there are ongoing concurrent lockless page-table walks — the walkers just disable IRQs and walk.