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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3938C433EF for ; Mon, 31 Jan 2022 10:24:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 563426B0071; Mon, 31 Jan 2022 05:24:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 513596B0073; Mon, 31 Jan 2022 05:24:52 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 401E76B0074; Mon, 31 Jan 2022 05:24:52 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0103.hostedemail.com [216.40.44.103]) by kanga.kvack.org (Postfix) with ESMTP id 312946B0071 for ; Mon, 31 Jan 2022 05:24:52 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E522E90F77 for ; Mon, 31 Jan 2022 10:24:51 +0000 (UTC) X-FDA: 79090198782.13.A080BBB Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf21.hostedemail.com (Postfix) with ESMTP id 6E3D81C0002 for ; Mon, 31 Jan 2022 10:24:51 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 46283210FF; Mon, 31 Jan 2022 10:24:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1643624690; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=0hz3FVY2lD48V2ZTs1+H/0RTN7r8b6FNhKGlpEPpz9E=; b=i6Qyz0PTXKJ3XKNRimsaM9gR6PIQS+yhAtKrfdOLffZRt63ky/wDOUXpvLJsEXA217lcIS jAsuj/sR2a19yrcKUCNU7tJoepMREw9nkQ762UfdlPjCHsgaytbDrx9icLfWC/W8wf3bBB HLbCfi//fWOOk841kUiKI7xoS4K7qKs= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 7D597A3B83; Mon, 31 Jan 2022 10:24:49 +0000 (UTC) Date: Mon, 31 Jan 2022 11:24:48 +0100 From: Michal Hocko To: Wei Yang Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memory_hotplug: build zonelist for managed_zone Message-ID: References: <20220127012023.18095-1-richard.weiyang@gmail.com> <20220129002628.2cwr35glahq5f5md@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220129002628.2cwr35glahq5f5md@master> X-Rspam-User: nil X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6E3D81C0002 X-Stat-Signature: ttzc763qxdof1t4zs77gq99dugwyc34u Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=i6Qyz0PT; spf=pass (imf21.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-HE-Tag: 1643624691-896390 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 Sat 29-01-22 00:26:28, Wei Yang wrote: > On Thu, Jan 27, 2022 at 09:28:17AM +0100, Michal Hocko wrote: > >On Thu 27-01-22 01:20:23, Wei Yang wrote: > >> During memory hotplug, when online/offline a zone, we need to rebuild > >> the zonelist for all node. There are two checks to decide whether a zone > >> would be added to zonelist: > >> > >> * one in online_pages/offline_pages to decide necessity > >> * one in build_zonerefs_node to do real add > >> > >> Currently we use different criteria at these two places, which is > >> different from the original behavior. > >> > >> Originally during memory hotplug, zonelist is re-built when zone hasn't > >> been populated. This in introduced in 'commit 6811378e7d8b ("[PATCH] > >> wait_table and zonelist initializing for memory hotadd: update zonelists")'. > >> And at that moment, build_zonelists_node() also use populated_zone() to > >> decide whether the zone should be added to zonelist. > >> > >> While in 'commit 6aa303defb74 ("mm, vmscan: only allocate and reclaim > >> from zones with pages managed by the buddy allocator")', > >> build_zonelists_node() changed to use managed_zone() to add zonelist. > >> But we still use populated_zone() to decide the necessity. > >> > >> This patch restore the original behavior by using the same criteria to > >> add a zone in zonelist during memory hotplug. > > > >Why? > > > > In case we online a populated zone, but not managed. Then this zone will not > be in zonelist. Right? yeah. We can theoretically end up with a zone without any managed menory on the zonelists. But my primary question is why do we need this change? Does it fix any existing problem? Does it make the code easier to read/understand? Does it improve performance? Every patch should have a justification. Your changelog merely lists the history and then states the new behavior without any explanation of why that is needed or desired. See? -- Michal Hocko SUSE Labs