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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 818D6C433DB for ; Thu, 21 Jan 2021 19:10:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C7D523A1C for ; Thu, 21 Jan 2021 19:10:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726969AbhAUTJ6 (ORCPT ); Thu, 21 Jan 2021 14:09:58 -0500 Received: from foss.arm.com ([217.140.110.172]:44108 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726292AbhAUTIf (ORCPT ); Thu, 21 Jan 2021 14:08:35 -0500 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 DBD39139F; Thu, 21 Jan 2021 10:59:40 -0800 (PST) Received: from [10.57.39.58] (unknown [10.57.39.58]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D91463F66E; Thu, 21 Jan 2021 10:59:38 -0800 (PST) Subject: Re: [PATCH 0/1] mm: Optimizing hugepage zeroing in arm64 To: Will Deacon , Prathu Baronia Cc: Prathu Baronia , Catalin Marinas , Anshuman Khandual , linux-kernel@vger.kernel.org, chintan.pandya@oneplus.com, "glider@google.com" , Andrey Konovalov , Geert Uytterhoeven , Andrew Morton , Vincenzo Frascino , linux-arm-kernel@lists.infradead.org References: <20210121165153.17828-1-prathu.baronia@oneplus.com> <20210121174616.GA22740@willie-the-truck> From: Robin Murphy Message-ID: Date: Thu, 21 Jan 2021 18:59:37 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210121174616.GA22740@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-21 17:46, Will Deacon wrote: > On Thu, Jan 21, 2021 at 10:21:50PM +0530, Prathu Baronia wrote: >> This patch removes the unnecessary kmap calls in the hugepage zeroing path and >> improves the timing by 62%. >> >> I had proposed a similar change in Apr-May'20 timeframe in memory.c where I >> proposed to clear out a hugepage by directly calling a memset over the whole >> hugepage but got the opposition that the change was not architecturally neutral. >> >> Upon revisiting this now I see significant improvement by removing around 2k >> barrier calls from the zeroing path. So hereby I propose an arm64 specific >> definition of clear_user_highpage(). > > Given that barrier() is purely a thing for the compiler, wouldn't the same > change yield a benefit on any other architecture without HIGHMEM? In which > case, I think this sort of change belongs in the core code if it's actually > worthwhile. I would have thought it's more the constant manipulation of the preempt and pagefault counts, rather than the compiler barriers between them, that has the impact. Either way, if arm64 doesn't need to be atomic WRT preemption when clearing parts of hugepages then I also can't imagine that anyone else (at least for !HIGHMEM) would either. Robin.