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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 8CD09C47094 for ; Tue, 8 Jun 2021 01:41:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5E29E61278 for ; Tue, 8 Jun 2021 01:41:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231303AbhFHBnG (ORCPT ); Mon, 7 Jun 2021 21:43:06 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:4386 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231209AbhFHBnF (ORCPT ); Mon, 7 Jun 2021 21:43:05 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4FzXsr6cwDz6vQZ; Tue, 8 Jun 2021 09:37:20 +0800 (CST) Received: from [10.174.176.210] (10.174.176.210) 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 15.1.2176.2; Tue, 8 Jun 2021 09:41:10 +0800 Subject: Re: [PATCH 1/2] mm/zbud: reuse unbuddied[0] as buddied in zbud_pool To: Andrew Morton CC: , , , References: <20210605075141.1359969-1-linmiaohe@huawei.com> <20210605075141.1359969-2-linmiaohe@huawei.com> <20210607161010.94168ddc8128da6af1e45cea@linux-foundation.org> From: Miaohe Lin Message-ID: Date: Tue, 8 Jun 2021 09:41:10 +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: <20210607161010.94168ddc8128da6af1e45cea@linux-foundation.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.210] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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 2021/6/8 7:10, Andrew Morton wrote: > On Sat, 5 Jun 2021 15:51:40 +0800 Miaohe Lin wrote: > >> Since commit 9d8c5b5284e4 ("mm: zbud: fix condition check on allocation >> size"), zbud_pool.unbuddied[0] is always unused. We can reuse it as buddied >> field to save some possible memory. >> >> ... >> >> --- a/mm/zbud.c >> +++ b/mm/zbud.c >> @@ -96,7 +96,7 @@ >> struct zbud_pool { >> spinlock_t lock; >> struct list_head unbuddied[NCHUNKS]; >> - struct list_head buddied; >> +#define buddied unbuddied[0] >> struct list_head lru; >> u64 pages_nr; >> const struct zbud_ops *ops; > > That looks a bit hacky. Can we at least have a comment explaining > what's going on? > > Would it be better to implement this with a union, rather than a #define? It seems union is better and comment is necessary. Will try to do this. Many thanks for your comment and reply! > . >