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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 AD425C433C1 for ; Thu, 25 Mar 2021 14:40:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8553861A2A for ; Thu, 25 Mar 2021 14:40:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231409AbhCYOkd (ORCPT ); Thu, 25 Mar 2021 10:40:33 -0400 Received: from mx2.suse.de ([195.135.220.15]:47874 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230239AbhCYOkG (ORCPT ); Thu, 25 Mar 2021 10:40:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1616683205; 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=kysqydu6n/BcioxbRVAh8G87sWEE9K41NwnN+9Mu1XY=; b=Syb5a3qJ58DcnqHkieD37jiATjK2+yHARp5LvfjoZ5j7NkEU8FWPFxER5cKlLesmsQvEWD EkUwqX5Q569ZT6p5ING+ueNrqmYU6qN7p+g04n+/oBVLEuXpVIvA4SVOTGQTVqvMKsUOJ/ rdjKyxIncpqpSQ5gKTsrk7UvuUZOEyU= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 65FFFADAA; Thu, 25 Mar 2021 14:40:05 +0000 (UTC) Date: Thu, 25 Mar 2021 15:40:04 +0100 From: Michal Hocko To: Oscar Salvador Cc: David Hildenbrand , Andrew Morton , Anshuman Khandual , Vlastimil Babka , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Message-ID: References: <3bc4168c-fd31-0c9a-44ac-88e25d524eef@redhat.com> <9591a0b8-c000-2f61-67a6-4402678fe50b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 25-03-21 15:02:26, Oscar Salvador wrote: > On Thu, Mar 25, 2021 at 01:26:34PM +0100, Michal Hocko wrote: > > Yeah, David has raised the contiguous flag for zone already. And to be > > completely honest I fail to see why we should shape a design based on an > > optimization. If anything we can teach set_zone_contiguous to simply > > ignore zone affiliation of vmemmap pages. I would be really curious if > > that would pose any harm to the compaction code as they are reserved and > > compaction should simply skip them. > > No, compaction code is clever enough to skip over those pages as it > already does for any Reserved page. > My comment was more towards having the zone contiguous. > > I know it is an optimization, but > > commit 7cf91a98e607c2f935dbcc177d70011e95b8faff > Author: Joonsoo Kim > Date: Tue Mar 15 14:57:51 2016 -0700 > > mm/compaction: speed up pageblock_pfn_to_page() when zone is contiguous > > talks about 30% of improvment. I am not sure if those numbers would > still hold nowawadys, but it feels wrong to drop it to the ground when > we can do better there, and IMHO, it does not overly complicate things. Again, do not shape design around an optimization. If this turns out a real problem then it can be handled on top. > > THere is nothing like a proper zone. > > I guess not, but for me it makes sense that vmemmap pages stay within > the same zone as the pages they describe. This is not the case for normal hotplug so why this should be any different. > Of course, this is a matter of opinions/taste. > > > Not sure what you are referring to but if you have prior to f1dd2cd13c4b > > ("mm, memory_hotplug: do not associate hotadded memory to zones until > > online") then this was entirely a different story. Users do care where > > they memory goes because that depends on the usecase but do they care > > about vmemmap? > > As I said, that is not what I am worried about. > Users do not really care where those pages end up, that is transparent > to them (wrt. vmemmap pages), but we (internally) kind of do. > > So, as I said, I see advantatges of using your way, but I see downsides > as: > > - I would like to consider zone, and for that we would have to pull > some of the functions that check for the zone at an aearly stage, and > the mere thought sounds ugly. This is impossible and whatever kind of heuristic you come up with might be wrong. > - Section containing vmemmap can remain offline and would have to come > up to sort that out Yes, this is a problem indeed and as I've said in other email this would be a problem for your initial implementation as well if the memory block is still offline. I suspect we need to treat these Vmemmap pages as online (via pfn_to_online_page). -- Michal Hocko SUSE Labs