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 B6B61C2D0A8 for ; Mon, 28 Sep 2020 07:58:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0F49E2311C for ; Mon, 28 Sep 2020 07:58:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F49E2311C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 41DC78E0003; Mon, 28 Sep 2020 03:58:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F6878E0001; Mon, 28 Sep 2020 03:58:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 332528E0003; Mon, 28 Sep 2020 03:58:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0125.hostedemail.com [216.40.44.125]) by kanga.kvack.org (Postfix) with ESMTP id 1ED3C8E0001 for ; Mon, 28 Sep 2020 03:58:30 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id C4F3D180AD804 for ; Mon, 28 Sep 2020 07:58:29 +0000 (UTC) X-FDA: 77311717938.30.kiss03_4907f462717f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 9606E180B3C83 for ; Mon, 28 Sep 2020 07:58:29 +0000 (UTC) X-HE-Tag: kiss03_4907f462717f X-Filterd-Recvd-Size: 2516 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 28 Sep 2020 07:58:29 +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-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 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