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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 59CDBC4740A for ; Mon, 9 Sep 2019 18:13:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D4B021A4A for ; Mon, 9 Sep 2019 18:13:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405488AbfIISMm (ORCPT ); Mon, 9 Sep 2019 14:12:42 -0400 Received: from mga02.intel.com ([134.134.136.20]:24313 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405425AbfIISMe (ORCPT ); Mon, 9 Sep 2019 14:12:34 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Sep 2019 11:12:34 -0700 X-IronPort-AV: E=Sophos;i="5.64,486,1559545200"; d="scan'208";a="178428271" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Sep 2019 11:12:33 -0700 Message-ID: <576de40e00083206bdb0c2e9f04fe34dd406e6b3.camel@linux.intel.com> Subject: Re: [PATCH v9 3/8] mm: Move set/get_pcppage_migratetype to mmzone.h From: Alexander Duyck To: "Kirill A. Shutemov" , Alexander Duyck Cc: virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, mst@redhat.com, catalin.marinas@arm.com, david@redhat.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, will@kernel.org, linux-arm-kernel@lists.infradead.org, osalvador@suse.de, yang.zhang.wz@gmail.com, pagupta@redhat.com, konrad.wilk@oracle.com, nitesh@redhat.com, riel@surriel.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, ying.huang@intel.com, pbonzini@redhat.com, dan.j.williams@intel.com, fengguang.wu@intel.com, kirill.shutemov@linux.intel.com Date: Mon, 09 Sep 2019 11:12:33 -0700 In-Reply-To: References: <20190907172225.10910.34302.stgit@localhost.localdomain> <20190907172528.10910.37051.stgit@localhost.localdomain> <20190909095608.jwachx3womhqmjbl@box> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-09-09 at 11:01 -0700, Alexander Duyck wrote: > On Mon, 2019-09-09 at 12:56 +0300, Kirill A. Shutemov wrote: > > On Sat, Sep 07, 2019 at 10:25:28AM -0700, Alexander Duyck wrote: > > > From: Alexander Duyck > > > > > > In order to support page reporting it will be necessary to store and > > > retrieve the migratetype of a page. To enable that I am moving the set and > > > get operations for pcppage_migratetype into the mm/internal.h header so > > > that they can be used outside of the page_alloc.c file. > > > > > > Reviewed-by: Dan Williams > > > Signed-off-by: Alexander Duyck > > > > I'm not sure that it's great idea to export this functionality beyond > > mm/page_alloc.c without any additional safeguards. How would we avoid to > > messing with ->index when the page is not in the right state of its > > life-cycle. Can we add some VM_BUG_ON()s here? > > I am not sure what we would need to check on though. There are essentially > 2 cases where we are using this. The first is the percpu page lists so the > value is set either as a result of __rmqueue_smallest or > free_unref_page_prepare. The second one which hasn't been added yet is for > the Reported pages case which I add with patch 6. > > When I use it for page reporting I am essentially using the Reported flag > to identify what pages in the buddy list will have this value set versus > those that may not. I didn't explicitly define it that way, but that is > how I am using it so that the value cannot be trusted unless the Reported > flag is set. I guess the alternative would be to just treat the ->index value as the index within the boundary array, and not use the per-cpu list functions. Doing that might make things a bit more clear since all we are really doing is storing the index into the boundary list the page is contained in. I could probably combine the value of order and migratetype and save myself a few cycles in the process by just saving the index into the array directly.