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=-5.3 required=3.0 tests=BAYES_00, 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 62758C2D0A8 for ; Mon, 28 Sep 2020 07:58:41 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E804E22262 for ; Mon, 28 Sep 2020 07:58:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E804E22262 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kMo3L-0002gv-J8; Mon, 28 Sep 2020 07:58:31 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kMo3K-0002gq-Ex for xen-devel@lists.xenproject.org; Mon, 28 Sep 2020 07:58:30 +0000 X-Inumbo-ID: fe3cd8d0-ab64-42c7-beb2-536d692dee03 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id fe3cd8d0-ab64-42c7-beb2-536d692dee03; Mon, 28 Sep 2020 07:58:28 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id DBD45B038; Mon, 28 Sep 2020 07:58:27 +0000 (UTC) Date: Mon, 28 Sep 2020 09:58:24 +0200 From: Oscar Salvador To: David Hildenbrand 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 , Alexander Duyck , Mel Gorman , Michal Hocko , Dave Hansen , Vlastimil Babka , Wei Yang , Mike Rapoport , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu Subject: Re: [PATCH RFC 4/4] mm/page_alloc: place pages to tail in __free_pages_core() Message-ID: <20200928075820.GA4082@linux> References: <20200916183411.64756-1-david@redhat.com> <20200916183411.64756-5-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200916183411.64756-5-david@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Wed, Sep 16, 2020 at 08:34:11PM +0200, David Hildenbrand wrote: > @@ -1523,7 +1524,13 @@ void __free_pages_core(struct page *page, unsigned int order) > > atomic_long_add(nr_pages, &page_zone(page)->managed_pages); > set_page_refcounted(page); > - __free_pages(page, order); > + > + /* > + * Bypass PCP and place fresh pages right to the tail, primarily > + * relevant for memory onlining. > + */ > + page_ref_dec(page); > + __free_pages_ok(page, order, FOP_TO_TAIL); Sorry, I must be missing something obvious here, but I am a bit confused here. I get the part of placing them at the tail so rmqueue_bulk() won't find them, but I do not get why we decrement page's refcount. IIUC, its refcount will be 0, but why do we want to do that? Another thing a bit unrelated... we mess three times with page's refcount (two before this patch). Why do we have this dance in place? Thanks -- Oscar Salvador SUSE L3