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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2EA0C54EE9 for ; Tue, 20 Sep 2022 08:46:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231324AbiITIqM (ORCPT ); Tue, 20 Sep 2022 04:46:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230238AbiITIpv (ORCPT ); Tue, 20 Sep 2022 04:45:51 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3D86E2A738; Tue, 20 Sep 2022 01:45:48 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6ED20106F; Tue, 20 Sep 2022 01:45:54 -0700 (PDT) Received: from [10.163.57.146] (unknown [10.163.57.146]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EE8EE3F73B; Tue, 20 Sep 2022 01:45:37 -0700 (PDT) Message-ID: <8c4f103b-8f04-d0ad-b30a-2db7e52b36a3@arm.com> Date: Tue, 20 Sep 2022 14:15:34 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3 4/4] arm64: support batched/deferred tlb shootdown during page reclamation Content-Language: en-US To: Barry Song <21cnbao@gmail.com> Cc: Yicong Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, catalin.marinas@arm.com, will@kernel.org, linux-doc@vger.kernel.org, corbet@lwn.net, peterz@infradead.org, arnd@arndb.de, linux-kernel@vger.kernel.org, darren@os.amperecomputing.com, yangyicong@hisilicon.com, huzhanyuan@oppo.com, lipeifeng@oppo.com, zhangshiming@oppo.com, guojian@oppo.com, realmz6@gmail.com, linux-mips@vger.kernel.org, openrisc@lists.librecores.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, wangkefeng.wang@huawei.com, xhao@linux.alibaba.com, prime.zeng@hisilicon.com, Barry Song , Nadav Amit , Mel Gorman References: <20220822082120.8347-1-yangyicong@huawei.com> <20220822082120.8347-5-yangyicong@huawei.com> <302febae-508c-d73e-8676-d51752946645@arm.com> From: Anshuman Khandual In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 9/20/22 09:09, Barry Song wrote: > On Tue, Sep 20, 2022 at 3:00 PM Anshuman Khandual > wrote: >> >> >> On 8/22/22 13:51, Yicong Yang wrote: >>> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) >>> +{ >>> + return true; >>> +} >> >> This needs to be conditional on systems, where there will be performance >> improvements, and should not just be enabled all the time on all systems. >> num_online_cpus() > X, which does not hold any cpu hotplug lock would be >> a good metric ? > > for a small system, i don't see how this patch will help, e.g. cpus <= 4; > so we can actually disable tlb-batch on small systems. Do not subscribe ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH based on NR_CPUS ? That might not help much as the default value is 256 for NR_CPUS. OR arch_tlbbatch_should_defer() checks on 1. online cpus (dont enable batched TLB if <= X) 2. ARM64_WORKAROUND_REPEAT_TLBI (dont enable batched TLB) > just need to check if we will have any race condition since hotplug will > make the condition true and false dynamically. If should_defer_flush() evaluate to be false, then ptep_clear_flush() clears and flushes the entry right away. This should not race with other queued up TLBI requests, which will be flushed separately. Wondering how there can be a race here !