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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 B61B3C2B9F4 for ; Fri, 25 Jun 2021 06:32:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95E3C6141F for ; Fri, 25 Jun 2021 06:32:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233169AbhFYGeb (ORCPT ); Fri, 25 Jun 2021 02:34:31 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:5077 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230097AbhFYGea (ORCPT ); Fri, 25 Jun 2021 02:34:30 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4GB6V604KZzXkxY; Fri, 25 Jun 2021 14:26:54 +0800 (CST) Received: from [10.174.177.120] (10.174.177.120) 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; Fri, 25 Jun 2021 14:32:06 +0800 Subject: Re: [Phishing Risk] [External] [PATCH 2/3] mm/zsmalloc.c: combine two atomic ops in zs_pool_dec_isolated() To: Muchun Song CC: Andrew Morton , Minchan Kim , , , LKML , Linux Memory Management List References: <20210624123930.1769093-1-linmiaohe@huawei.com> <20210624123930.1769093-3-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <1b38b33f-316e-1816-216f-9923f612ceb6@huawei.com> Date: Fri, 25 Jun 2021 14:32:05 +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: [10.174.177.120] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) 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 2021/6/25 13:01, Muchun Song wrote: > On Thu, Jun 24, 2021 at 8:40 PM Miaohe Lin wrote: >> >> atomic_long_dec_and_test() is equivalent to atomic_long_dec() and >> atomic_long_read() == 0. Use it to make code more succinct. > > Actually, they are not equal. atomic_long_dec_and_test implies a > full memory barrier around it but atomic_long_dec and atomic_long_read > don't. > Many thanks for comment. They are indeed not completely equal as you said. What I mean is they can do the same things we want in this specified context. Thanks again. > That RMW operations that have a return value is equal to the following. > > smp_mb__before_atomic() > non-RMW operations or RMW operations that have no return value > smp_mb__after_atomic() > > Thanks. > >> >> Signed-off-by: Miaohe Lin >> --- >> mm/zsmalloc.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c >> index 1476289b619f..0b4b23740d78 100644 >> --- a/mm/zsmalloc.c >> +++ b/mm/zsmalloc.c >> @@ -1828,13 +1828,12 @@ static void putback_zspage_deferred(struct zs_pool *pool, >> static inline void zs_pool_dec_isolated(struct zs_pool *pool) >> { >> VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0); >> - atomic_long_dec(&pool->isolated_pages); >> /* >> * There's no possibility of racing, since wait_for_isolated_drain() >> * checks the isolated count under &class->lock after enqueuing >> * on migration_wait. >> */ >> - if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying) >> + if (atomic_long_dec_and_test(&pool->isolated_pages) && pool->destroying) >> wake_up_all(&pool->migration_wait); >> } >> >> -- >> 2.23.0 >> > . >