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=unavailable 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 8EFFEC2B9F4 for ; Fri, 25 Jun 2021 08:46:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 06C32613EF for ; Fri, 25 Jun 2021 08:46:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06C32613EF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C256F6B0036; Fri, 25 Jun 2021 04:46:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BFC266B005D; Fri, 25 Jun 2021 04:46:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AC40B6B006C; Fri, 25 Jun 2021 04:46:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0077.hostedemail.com [216.40.44.77]) by kanga.kvack.org (Postfix) with ESMTP id 77F7A6B0036 for ; Fri, 25 Jun 2021 04:46:38 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9884685F19B0 for ; Fri, 25 Jun 2021 08:46:38 +0000 (UTC) X-FDA: 78291615276.20.E04739C Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf07.hostedemail.com (Postfix) with ESMTP id 4FDFEA000263 for ; Fri, 25 Jun 2021 08:46:37 +0000 (UTC) Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4GB9TD4CcTzXkcs; Fri, 25 Jun 2021 16:41:20 +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 16:46:33 +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> <1b38b33f-316e-1816-216f-9923f612ceb6@huawei.com> From: Miaohe Lin Message-ID: <01117bc0-53b1-d81a-a4d8-2a1dbe5dcd94@huawei.com> Date: Fri, 25 Jun 2021 16:46:32 +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: dggems702-chm.china.huawei.com (10.3.19.179) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4FDFEA000263 X-Stat-Signature: t6tzedo1trjw9xfe6msqgdupeaqra3uw Authentication-Results: imf07.hostedemail.com; dkim=none; spf=pass (imf07.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-HE-Tag: 1624610797-223382 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/6/25 15:29, Muchun Song wrote: > On Fri, Jun 25, 2021 at 2:32 PM Miaohe Lin wrote: >> >> 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. > > I don't think so. Using individual operations can eliminate memory barriers. > We will pay for the barrier if we use atomic_long_dec_and_test here. The combination of atomic_long_dec and atomic_long_read usecase is rare and looks somehow weird. I think it's worth to do this with the cost of barrier. > >> >>> 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 >>>> >>> . >>> >> > . >