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 35662C3DA7A for ; Fri, 6 Jan 2023 06:23:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231635AbjAFGXs (ORCPT ); Fri, 6 Jan 2023 01:23:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231916AbjAFGXc (ORCPT ); Fri, 6 Jan 2023 01:23:32 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0615332253 for ; Thu, 5 Jan 2023 22:23:28 -0800 (PST) Received: from dggpemm500001.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4NpCsr1H5czRr14; Fri, 6 Jan 2023 14:21:52 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Fri, 6 Jan 2023 14:23:26 +0800 Message-ID: Date: Fri, 6 Jan 2023 14:23:25 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v2] mm: huge_memory: convert split_huge_pages_all() to use a folio Content-Language: en-US To: Andrew Morton CC: , , References: <20221230093020.9664-1-wangkefeng.wang@huawei.com> <20221230134535.240f49e0ad8bf6d82f8cc393@linux-foundation.org> <20230105190658.f5d9a4bc9619ad6bec91a973@linux-foundation.org> From: Kefeng Wang In-Reply-To: <20230105190658.f5d9a4bc9619ad6bec91a973@linux-foundation.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/1/6 11:06, Andrew Morton wrote: > On Tue, 3 Jan 2023 09:58:36 +0800 Kefeng Wang wrote: > >> >> >> On 2022/12/31 5:45, Andrew Morton wrote: >>> On Fri, 30 Dec 2022 17:30:20 +0800 Kefeng Wang wrote: >>> >>>> Straightforwardly convert split_huge_pages_all() to use a folio. >>>> >>>> ... >>>> >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -2932,6 +2932,7 @@ static void split_huge_pages_all(void) >>>> { >>>> struct zone *zone; >>>> struct page *page; >>>> + struct folio *folio; >>>> unsigned long pfn, max_zone_pfn; >>>> unsigned long total = 0, split = 0; >>>> >>>> @@ -2944,24 +2945,32 @@ static void split_huge_pages_all(void) >>>> int nr_pages; >>>> >>>> page = pfn_to_online_page(pfn); >>>> - if (!page || !get_page_unless_zero(page)) >>>> + if (!page || PageTail(page)) >>>> + continue; >>>> + folio = page_folio(page); >>>> + if (!folio_try_get(folio)) >>>> continue; >>>> >>>> - if (zone != page_zone(page)) >>>> + if (unlikely(page_folio(page) != folio)) >>>> + goto next; >>>> + >>>> + if (zone != folio_zone(folio)) >>>> goto next; >>> >>> I'm still not understanding the above hunk. Why is the >>> "page_folio(page) != folio" check added? Should it be commented? >> >> There is a comment in try_get_folio(), is it enough? > > Nobody would think to look at a private function in gup.c. Sorry，I mean that comment is to explain why adding a new recheck. > > I suggest this folio_try_get() rule be documented at the > folio_try_get() implementation site. > > Most callers do perform this check, but not the ones in vmscan.c ? Hope Matthew could give some advise, thanks