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 6C3D6C07E96 for ; Mon, 5 Jul 2021 03:27:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0CDFF613BA for ; Mon, 5 Jul 2021 03:27:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0CDFF613BA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B9F666B0011; Sun, 4 Jul 2021 23:27:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B34706B0036; Sun, 4 Jul 2021 23:27:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9C86E6B005D; Sun, 4 Jul 2021 23:27:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0188.hostedemail.com [216.40.44.188]) by kanga.kvack.org (Postfix) with ESMTP id 717E36B0011 for ; Sun, 4 Jul 2021 23:27:11 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 001871809DF51 for ; Mon, 5 Jul 2021 03:27:10 +0000 (UTC) X-FDA: 78327098262.20.AC7D511 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf23.hostedemail.com (Postfix) with ESMTP id 65CCC90000AC for ; Mon, 5 Jul 2021 03:27:10 +0000 (UTC) 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 3CD26D6E; Sun, 4 Jul 2021 20:27:09 -0700 (PDT) Received: from [10.163.88.246] (unknown [10.163.88.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 856513F5A1; Sun, 4 Jul 2021 20:27:07 -0700 (PDT) Subject: Re: [PATCH V2] mm/thp: Make ALLOC_SPLIT_PTLOCKS dependent on USE_SPLIT_PTE_PTLOCKS To: Matthew Wilcox Cc: linux-mm@kvack.org, akpm@linux-foundation.org, Vlastimil Babka , Randy Dunlap , linux-kernel@vger.kernel.org References: <1621409586-5555-1-git-send-email-anshuman.khandual@arm.com> <9d1ce685-e0fd-febd-5ff2-179f7fa6e3fa@arm.com> From: Anshuman Khandual Message-ID: <45c1feaa-4bab-91d1-6962-81549d2b6d00@arm.com> Date: Mon, 5 Jul 2021 08:57:54 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf23.hostedemail.com; dkim=none; spf=pass (imf23.hostedemail.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com; dmarc=pass (policy=none) header.from=arm.com X-Stat-Signature: qmmjezy5zrnkdbusxjbdxqc5fpgojej1 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 65CCC90000AC X-HE-Tag: 1625455630-126815 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: On 7/1/21 6:27 PM, Matthew Wilcox wrote: > On Thu, Jul 01, 2021 at 10:51:27AM +0530, Anshuman Khandual wrote: >> >> >> On 5/20/21 4:47 PM, Matthew Wilcox wrote: >>> On Wed, May 19, 2021 at 01:03:06PM +0530, Anshuman Khandual wrote: >>>> Split ptlocks need not be defined and allocated unless they are being used. >>>> ALLOC_SPLIT_PTLOCKS is inherently dependent on USE_SPLIT_PTE_PTLOCKS. This >>>> just makes it explicit and clear. While here drop the spinlock_t element >>>> from the struct page when USE_SPLIT_PTE_PTLOCKS is not enabled. >>> >>> I didn't spot this email yesterday. I'm not a fan. Isn't struct page >>> already complicated enough without adding another ifdef to it? Surely >>> there's a better way than this. >> >> This discussion thread just got dropped off the radar, sorry about it. >> None of the spinlock_t elements are required unless split ptlocks are >> in use. I understand your concern regarding yet another #ifdef in the >> struct page definition. But this change is simple and minimal. Do you >> have any other particular alternative in mind which I could explore ? > > Do nothing? I don't understand what problem you're trying to solve. Currently there is an element (spinlock_t ptl) in the struct page for page table lock. Although a struct page based spinlock is not even required in case USE_SPLIT_PTE_PTLOCKS evaluates to be false. Is not that something to be fixed here i.e drop the splinlock_t element if not required ? The problem is USE_SPLIT_PTE_PTLOCKS and ALLOC_SPLIT_PTLOCKS get evaluated independently, although they are inherently dependent. ALLOC_SPLIT_PTLOCKS could just be set to 0, when USE_SPLIT_PTE_PTLOCKS evaluates to be 0. This patch makes that dependency explicit and also fixes the above situation.