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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 9DBB6C0044C for ; Wed, 7 Nov 2018 10:28:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7126A2085B for ; Wed, 7 Nov 2018 10:28:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7126A2085B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730526AbeKGT6Y (ORCPT ); Wed, 7 Nov 2018 14:58:24 -0500 Received: from mx2.suse.de ([195.135.220.15]:59436 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726218AbeKGT6Y (ORCPT ); Wed, 7 Nov 2018 14:58:24 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0762AAF9B; Wed, 7 Nov 2018 10:28:38 +0000 (UTC) Date: Wed, 7 Nov 2018 11:28:37 +0100 From: Michal Hocko To: Vlastimil Babka Cc: Konstantin Khlebnikov , Arun KS , keescook@chromium.org, minchan@kernel.org, getarunks@gmail.com, gregkh@linuxfoundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, julia.lawall@lip6.fr Subject: Re: [PATCH v1 0/4]mm: convert totalram_pages, totalhigh_pages and managed pages to atomic Message-ID: <20181107102837.GC27423@dhcp22.suse.cz> References: <1540551662-26458-1-git-send-email-arunks@codeaurora.org> <9b210d4cc9925caf291412d7d45f16d7@codeaurora.org> <63d9f48c-e39f-d345-0fb6-2f04afe769a2@yandex-team.ru> <08a61c003eed0280fd82f6200debcbca@codeaurora.org> <10c88df6-dbb1-7490-628c-055d59b5ad8e@yandex-team.ru> <22fa2222012341a54f6b0b6aea341aa2@codeaurora.org> <89a259aa-156e-041c-b3bc-266824acb173@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <89a259aa-156e-041c-b3bc-266824acb173@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 07-11-18 09:50:10, Vlastimil Babka wrote: > On 11/7/18 8:02 AM, Konstantin Khlebnikov wrote: [...] > > Could you point what exactly are you fixing with this set? > > > > from v2: > > > > > totalram_pages, zone->managed_pages and totalhigh_pages updates > > > are protected by managed_page_count_lock, but readers never care > > > about it. Convert these variables to atomic to avoid readers > > > potentially seeing a store tear. > > > > This? > > > > > > Aligned unsigned long almost always stored at once. > > The point is "almost always", so better not rely on it :) But the main > motivation was that managed_page_count_lock handling was complicating > Arun's "memory_hotplug: Free pages as higher order" patch and it seemed > a better idea to just remove and convert this to atomics, with > preventing potential store-to-read tearing as a bonus. And more importantly the lock itself seems bogus as mentioned here http://lkml.kernel.org/r/20181106141732.GR27423@dhcp22.suse.cz > It would be nice to mention it in the changelogs though. agreed -- Michal Hocko SUSE Labs