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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25275C433EF for ; Sat, 25 Jun 2022 03:18:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231924AbiFYDSS (ORCPT ); Fri, 24 Jun 2022 23:18:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58100 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231679AbiFYDSP (ORCPT ); Fri, 24 Jun 2022 23:18:15 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7A79E2ED67 for ; Fri, 24 Jun 2022 20:18:13 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4LVJzM6dL8z1KCD2; Sat, 25 Jun 2022 11:15:59 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sat, 25 Jun 2022 11:18:10 +0800 Subject: Re: [PATCH 14/16] mm/huge_memory: fix comment of page_deferred_list To: Zach O'Keefe CC: Muchun Song , , , , , References: <20220622170627.19786-1-linmiaohe@huawei.com> <20220622170627.19786-15-linmiaohe@huawei.com> <0b1a1633-2e07-87df-b707-3058353f5609@huawei.com> From: Miaohe Lin Message-ID: <22e8cac7-2d3d-6099-9875-70e2ea007343@huawei.com> Date: Sat, 25 Jun 2022 11:18:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/25 1:09, Zach O'Keefe wrote: > On 23 Jun 20:26, Miaohe Lin wrote: >> On 2022/6/23 15:24, Muchun Song wrote: >>> On Thu, Jun 23, 2022 at 01:06:25AM +0800, Miaohe Lin wrote: >>>> The current comment is confusing because if global or memcg deferred list >>>> in the second tail page is occupied by compound_head, why we still use >>>> page[2].deferred_list here? I think it wants to say that Global or memcg >>>> deferred list in the first tail page is occupied by compound_mapcount and >>>> compound_pincount so we use the second tail page's deferred_list instead. >>>> >>>> Signed-off-by: Miaohe Lin >>>> --- >>>> include/linux/huge_mm.h | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>>> index 12b297f9951d..2e8062b3417a 100644 >>>> --- a/include/linux/huge_mm.h >>>> +++ b/include/linux/huge_mm.h >>>> @@ -294,8 +294,8 @@ static inline bool thp_migration_supported(void) >>>> static inline struct list_head *page_deferred_list(struct page *page) >>>> { >>>> /* >>>> - * Global or memcg deferred list in the second tail pages is >>>> - * occupied by compound_head. >>>> + * Global or memcg deferred list in the first tail page is >>>> + * occupied by compound_mapcount and compound_pincount. >>>> */ >>> >>> The structure of "struct page" seems to have told us the information that >>> we resue the 2nd tail page to be used as deferred_list. I am not sure the >> >> Yes, it does. >> >>> value of those comments. Maybe better to remove them? >> >> IMHO above comment tries to tell us why deferred list in the second tail page is used >> instead of first tail page. But it should be fine to remove the above comments as they >> don't seem to provide much info (thought I'm not really sure). >> >> Thanks. >> > > Just a suggestion - feel free to disregard. Maybe we don't need to repeat the > comments in struct page, but maybe a "see organization of tail pages of compound > page in "struct page" definition" would at least point new people to where this > magic 2 comes from. Maybe an obvious place to check after you're familiar with > overloading struct page data for compound pages - but IMO it's not obvious for > newcomers. This is a good suggestion to me. Thanks! > >>> >>> Thanks. >>> >>>> return &page[2].deferred_list; >>>> } >>>> -- >>>> 2.23.0 >>>> >>>> >>> . >>> >> > . >