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 14431C433F5 for ; Tue, 8 Mar 2022 06:34:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244237AbiCHGfV (ORCPT ); Tue, 8 Mar 2022 01:35:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231716AbiCHGfR (ORCPT ); Tue, 8 Mar 2022 01:35:17 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79DA53CA5C for ; Mon, 7 Mar 2022 22:34:20 -0800 (PST) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4KCQQz1CQ7z1GCHB; Tue, 8 Mar 2022 14:29:31 +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 15.1.2308.21; Tue, 8 Mar 2022 14:34:17 +0800 Subject: Re: [PATCH 13/16] mm/migration: return errno when isolate_huge_page failed To: Baolin Wang , CC: , , , , , , , , , , , , , , , , , References: <20220304093409.25829-1-linmiaohe@huawei.com> <20220304093409.25829-14-linmiaohe@huawei.com> <3d286f44-e91d-b68d-63f2-e66529e3fa54@linux.alibaba.com> From: Miaohe Lin Message-ID: <257f4e4b-aaab-824c-9a68-6dc88d7f988f@huawei.com> Date: Tue, 8 Mar 2022 14:34:17 +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: <3d286f44-e91d-b68d-63f2-e66529e3fa54@linux.alibaba.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) 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 2022/3/8 9:32, Baolin Wang wrote: > > > On 3/7/2022 8:20 PM, Miaohe Lin wrote: >> On 2022/3/7 10:14, Baolin Wang wrote: >>> Hi Miaohe, >>> >>> On 3/4/2022 5:34 PM, Miaohe Lin wrote: >>>> We should return errno (-EBUSY here) when failed to isolate the huge page >>>> rather than always return 1 which could confuse the user. >>>> >>>> Signed-off-by: Miaohe Lin >>>> --- >>>>    mm/migrate.c | 6 ++---- >>>>    1 file changed, 2 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>> index 6c2dfed2ddb8..279940c0c064 100644 >>>> --- a/mm/migrate.c >>>> +++ b/mm/migrate.c >>>> @@ -1618,10 +1618,8 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr, >>>>            goto out_putpage; >>>>          if (PageHuge(page)) { >>>> -        if (PageHead(page)) { >>>> -            isolate_huge_page(page, pagelist); >>>> -            err = 1; >>>> -        } >>>> +        if (PageHead(page)) >>>> +            err = isolate_huge_page(page, pagelist) ? 1 : -EBUSY; >>> >>> Could you elaborate on which case the huge page isolation can be failed in this case? Or you met a real problem? Cause now we've got this head huge page refcnt, I can not see why we'll fail to isolate this huge page. >> >> IIUC, this could happen when hugepage is under migration which cleared HPageMigratable. Page refcnt cannot >> prevent isolate_huge_page from happening. Or am I miss something? > > Yes, that's possible. Thanks for your explanation. It will be better if you can copy the possible scenario description to the commit log to help other understand the issue. > Sounds reasonable. Will do. Many thanks for review. > Reviewed-by: Baolin Wang > .