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=-5.4 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,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 14F66C4727E for ; Mon, 5 Oct 2020 06:56:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7E772080A for ; Mon, 5 Oct 2020 06:56:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="S66gtJ8a" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725898AbgJEG4y (ORCPT ); Mon, 5 Oct 2020 02:56:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:36870 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725869AbgJEG4w (ORCPT ); Mon, 5 Oct 2020 02:56:52 -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=1601881010; h=from:from:reply-to:subject:subject: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=UNEm7Tn9UNlLqhlrULq94v99iXKf+1bbfGtGmTKX+7I=; b=S66gtJ8axc/8vLsDG0Y3zJ3DfLtemEkgIHkSLUIWIDdOmJTl5ozJHZlvC9eijR1y/3zccB UdINSjYVIGbyFe6FVLK6h+OkKKunrDQK6t3reRK6hhZJGiR0LMbXvjHxmXk9olvfWeq9+p FIB95YWX0cll+IESTIBsni+toXRKRnQ= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 93222B224; Mon, 5 Oct 2020 06:56:50 +0000 (UTC) Date: Mon, 5 Oct 2020 08:56:48 +0200 From: Michal Hocko To: David Hildenbrand , Mel Gorman , Vlastimil Babka Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org, Andrew Morton , Oscar Salvador , Alexander Duyck , Dave Hansen , Wei Yang , Mike Rapoport , Scott Cheloha , Michael Ellerman Subject: Re: [PATCH v1 3/5] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate() Message-ID: <20201005065648.GO4555@dhcp22.suse.cz> References: <20200928182110.7050-1-david@redhat.com> <20200928182110.7050-4-david@redhat.com> <20201002132404.GI4555@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Fri 02-10-20 17:20:09, David Hildenbrand wrote: > On 02.10.20 15:24, Michal Hocko wrote: > > On Mon 28-09-20 20:21:08, David Hildenbrand wrote: > >> Page isolation doesn't actually touch the pages, it simply isolates > >> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist. > >> > >> We already place pages to the tail of the freelists when undoing > >> isolation via __putback_isolated_page(), let's do it in any case > >> (e.g., if order <= pageblock_order) and document the behavior. > >> > >> Add a "to_tail" parameter to move_freepages_block() but introduce a > >> a new move_to_free_list_tail() - similar to add_to_free_list_tail(). > >> > >> This change results in all pages getting onlined via online_pages() to > >> be placed to the tail of the freelist. > > > > Is there anything preventing to do this unconditionally? Or in other > > words is any of the existing callers of move_freepages_block benefiting > > from adding to the head? > > 1. mm/page_isolation.c:set_migratetype_isolate() > > We move stuff to the MIGRATE_ISOLATE list, we don't care about the order > there. > > 2. steal_suitable_fallback(): > > I don't think we care too much about the order when already stealing > pageblocks ... and the freelist is empty I guess? > > 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() > > Not sure if we really care. Honestly, I have no idea. I can imagine that some atomic high order workloads (e.g. in net) might benefit from cache line hot pages but I am not sure this is really observable. If yes it would likely be better to have this documented than relying on wild guess. If we do not have any evidence then I would vote for simplicity first and go with unconditional add_to_tail which would simply your patch a bit. Maybe Vlastimil or Mel would have a better picture. -- Michal Hocko SUSE Labs