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=-6.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 49D50C432BE for ; Wed, 1 Sep 2021 08:05:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F2E46103A for ; Wed, 1 Sep 2021 08:05:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242908AbhIAIGr (ORCPT ); Wed, 1 Sep 2021 04:06:47 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:8995 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232072AbhIAIGo (ORCPT ); Wed, 1 Sep 2021 04:06:44 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4GzxRy4nFYzYwXJ; Wed, 1 Sep 2021 16:05:02 +0800 (CST) Received: from [10.174.178.75] (10.174.178.75) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Wed, 1 Sep 2021 16:05:44 +0800 Subject: Re: [PATCH 6/6] mm/page_alloc.c: avoid allocating highmem pages via alloc_pages_exact_nid() To: Vlastimil Babka , Matthew Wilcox CC: , , , , , References: <20210830141051.64090-1-linmiaohe@huawei.com> <20210830141051.64090-7-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: Date: Wed, 1 Sep 2021 16:05:44 +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: [10.174.178.75] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/9/1 0:37, Vlastimil Babka wrote: > On 8/31/21 03:56, Miaohe Lin wrote: >> On 2021/8/30 22:24, Matthew Wilcox wrote: >>> On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: >>>> Don't use with __GFP_HIGHMEM because page_address() cannot represent >>>> highmem pages without kmap(). Newly allocated pages would leak as >>>> page_address() will return NULL for highmem pages here. But It works >>>> now because the only caller does not specify __GFP_HIGHMEM now. >>> >>> This is a misunderstanding of how alloc_pages_exact() / >>> alloc_pages_exact_nid() work. You simply can't call them with >>> GFP_HIGHMEM. >>> >> >> Yep, they can't work with GFP_HIGHMEM. So IMO it might be better to >> get rid of GFP_HIGHMEM explicitly or add a comment to clarify this >> situation to avoid future misbehavior. But this may be a unnecessary >> worry... Do you prefer to not change anything here? > > I agree with the suggestion below... > >> Many thanks. >> >>> If you really must change anything here, >>> s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both >>> alloc_pages_exact() and alloc_pages_exact_nid(). > > ... which means __GFP_HIGHMEM would be stripped and additionally there would > be a warning. > Looks good for me. Will do. Many thanks! > . >