From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 0F3A96B04EE for ; Wed, 7 Nov 2018 05:28:41 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id x98-v6so9288361ede.0 for ; Wed, 07 Nov 2018 02:28:41 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c6-v6si283331ejd.9.2018.11.07.02.28.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Nov 2018 02:28:39 -0800 (PST) Date: Wed, 7 Nov 2018 11:28:37 +0100 From: Michal Hocko 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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