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=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7C0A1C2B9F4 for ; Fri, 25 Jun 2021 05:02:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56AB361420 for ; Fri, 25 Jun 2021 05:02:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233110AbhFYFE7 (ORCPT ); Fri, 25 Jun 2021 01:04:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42284 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233080AbhFYFE4 (ORCPT ); Fri, 25 Jun 2021 01:04:56 -0400 Received: from mail-pl1-x62e.google.com (mail-pl1-x62e.google.com [IPv6:2607:f8b0:4864:20::62e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4436C061574 for ; Thu, 24 Jun 2021 22:02:36 -0700 (PDT) Received: by mail-pl1-x62e.google.com with SMTP id y13so4110528plc.8 for ; Thu, 24 Jun 2021 22:02:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=5r9y0DuPKIkFXl5HZacGmA+FHZr5TguPZuuivsw9axA=; b=fuQDLirew2DROVEKhVG07H1CT9vGGgdcQSbx4lECRGyyaP5bgiifTAzxWJ5P2nf/mw z48BgZG1R7uPtDmrrrxs25+zVyzIIWfk0UHF1r43+1FcA2ktAzKxQulx8m4y864I8KX2 bR1fFOoZvdw7BPZODmSS08Lhmr7e0igQjkEYm1ZZzaF3bjvpaE4uIcXb/b3tCdeJCF1O wNipujLgsYrbszeFZskZNnAX4+Brf1A4uqacrspKi6m72p8I9g9OIcG2ZzkRowUEyC9/ W/NeQ5qZ18vDxEfxh03TvyXPDp6MTbcR6+1xk8/9I6qpC9+KGy/6gzN8HoKnYQ3M4Iks sNdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=5r9y0DuPKIkFXl5HZacGmA+FHZr5TguPZuuivsw9axA=; b=HlrDSQDJ6G8l40t7euvHuhE2nflk9wtnzMN+nq44gK8VrkAmjFa1nzK75thLNkUM+D bdFvkZC+tJ7uDBuknGQeQlaF5qTFivnY0IoLF42OIw5v9Qs/CWGiJzYmqv+vlx7h7gRb 64u0gBju9kMQFhEYW33Nn7R7h/JC4tG3/eYRvOl9jloIyEkWVRPQp68czhD82x9qIPvt DaKlBgsizlf9AUKbrskW4eVGH0AjNcpf5/ehHWiTBv9a2RzAP32Mh8z+SO2CauMr3ErQ IkOGLKhQvYFsweYmmbMyBq6cgBFYcU2TwXsWdU2fxQnfzcnA0mRjRr6/oopgBU5Lst7R KgDA== X-Gm-Message-State: AOAM532DDwHS4aFbRuREFRm79KCmv+o+eWROMiUUDMblCkpSGjRrAR07 ZeyaN/QXX1oK9bXOnmVnlKofCDTzlal0C1/QXLkutQ== X-Google-Smtp-Source: ABdhPJxETDHcgLBIFXu00r/zhM7WdGEx7akqu9B5kK/m2vplDtGR6sW7EOilwwcpTb74C9VYycebasMwyL63SXvAKiM= X-Received: by 2002:a17:90a:14a4:: with SMTP id k33mr6617767pja.13.1624597356423; Thu, 24 Jun 2021 22:02:36 -0700 (PDT) MIME-Version: 1.0 References: <20210624123930.1769093-1-linmiaohe@huawei.com> <20210624123930.1769093-3-linmiaohe@huawei.com> In-Reply-To: <20210624123930.1769093-3-linmiaohe@huawei.com> From: Muchun Song Date: Fri, 25 Jun 2021 13:01:53 +0800 Message-ID: Subject: Re: [Phishing Risk] [External] [PATCH 2/3] mm/zsmalloc.c: combine two atomic ops in zs_pool_dec_isolated() To: Miaohe Lin Cc: Andrew Morton , Minchan Kim , ngupta@vflare.org, senozhatsky@chromium.org, LKML , Linux Memory Management List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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 >