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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 D128EC43331 for ; Sat, 28 Mar 2020 00:26:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A3A46206F6 for ; Sat, 28 Mar 2020 00:26:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="u89NMh1A" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726781AbgC1A0V (ORCPT ); Fri, 27 Mar 2020 20:26:21 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:35617 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726281AbgC1A0V (ORCPT ); Fri, 27 Mar 2020 20:26:21 -0400 Received: by mail-wr1-f67.google.com with SMTP id d5so13953242wrn.2 for ; Fri, 27 Mar 2020 17:26:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:reply-to:references:mime-version :content-disposition:in-reply-to:user-agent; bh=o34z7NV9hLhlnbHsIbZ5TkmJUG3sU9ivdCVdSN9yfiw=; b=u89NMh1ACxIa7THDFh2QEdGWWv/ReIu4L4xooWDijmg+kY6Ufvwqve4POMnMMMhstd p8p9N/H0qK+EomSqkcsCrcc5ixTRqVPTMWdZEacxGu7jPQjhXnTd2UhxBI0AutporTHI rE3TbZbJ0aCGgcIlnFORqdH3XsZUQpu9VUuSZ5lanCi4Bx8V1zgH1Lf3jjXgltkufJ/J py4FBX9u1BDACzJdtLCqac5uZLIISY4NAK/TIKeX0H72CE5Xe60o0a3MBUbLWbQ23NyN hpytQzQSMtBAqt2i4j7nMezWvWwABluHCwJ6fPkWMaoejvxPyTn+5fbBe56JT1l91zTG bJig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:reply-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=o34z7NV9hLhlnbHsIbZ5TkmJUG3sU9ivdCVdSN9yfiw=; b=H2P7KO3hz/ANVhxvbjiEplp0C57GDosuIxLHJ3VgE7ih6a3OyxnzuJMikYpQHh+EmR OGkTWooU7/f593tZ+lHW+ZD6rqkE6pv2FTFwBCqXP7JUDFqvB1Vd6tEqk6P6bQsSx5bJ 3geKKgNWrJkY4ZF+0TzIURzYBdQMWzzA3PfF/38wj0R05Vbt1WJ7HBznflDQLIR1w+Le 4DKxRP63T+gHy+StGIBM6NUUd4q7fsM2WRT3KwxuApUskM+S3oxKS95cNwmrmheL1QHB uw19cdCEDkR76m05izRyIvm5fy5PbhnygtXtrzZ3UB04OJ+kKU36EZC+ZiwQbgFh7ggt I1wg== X-Gm-Message-State: ANhLgQ37DvyUsXPcz6ogLBpehEmHCaoPGizJiY1QQy2owWpM8hI+vUYT jsMOLTts1II+aff5Zn3YR28= X-Google-Smtp-Source: ADFU+vsNAURVsNTvCfnn3ERfF0eMVyH3ZDYFdxGFYHDbiNO4vgn0qMkASHLy6F1zaGRi3RvCXSbghA== X-Received: by 2002:adf:f892:: with SMTP id u18mr2063766wrp.367.1585355179041; Fri, 27 Mar 2020 17:26:19 -0700 (PDT) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id u8sm9977687wrn.69.2020.03.27.17.26.18 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 27 Mar 2020 17:26:18 -0700 (PDT) Date: Sat, 28 Mar 2020 00:26:16 +0000 From: Wei Yang To: John Hubbard Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca, david@redhat.com Subject: Re: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero Message-ID: <20200328002616.kjtf7dpkqbugyzi2@master> Reply-To: Wei Yang References: <20200327220121.27823-1-richard.weiyang@gmail.com> <20200327220121.27823-2-richard.weiyang@gmail.com> <4c9d8138-d379-810f-64e7-0d018ed019df@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4c9d8138-d379-810f-64e7-0d018ed019df@nvidia.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 27, 2020 at 03:37:57PM -0700, John Hubbard wrote: >On 3/27/20 3:01 PM, Wei Yang wrote: >> Since we always clear node_order before getting it, we can leverage >> compiler to do this instead of at run time. >> >> Signed-off-by: Wei Yang >> --- >> mm/page_alloc.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index dfcf2682ed40..49dd1f25c000 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -5585,7 +5585,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat) >> static void build_zonelists(pg_data_t *pgdat) >> { >> - static int node_order[MAX_NUMNODES]; >> + static int node_order[MAX_NUMNODES] = {0}; > > >Looks wrong: now the single instance of node_order is initialized just once by >the compiler. And that means that only the first caller of this function >gets a zeroed node_order array... > What a shame on me. You are right, I miss the static word. Well, then I am curious about why we want to define it as static. Each time we call this function, node_order would be set to 0 and find_next_best_node() would sort a proper value into it. I don't see the reason to reserve it in a global area and be used next time. My suggestion is to remove the static and define it {0} instead of memset every time. Is my understanding correct here? > >> int node, load, nr_nodes = 0; >> nodemask_t used_mask = NODE_MASK_NONE; >> int local_node, prev_node; >> @@ -5595,7 +5595,6 @@ static void build_zonelists(pg_data_t *pgdat) >> load = nr_online_nodes; >> prev_node = local_node; >> - memset(node_order, 0, sizeof(node_order)); > >...and all subsequent callers are left with whatever debris is remaining in >node_order. So this is not good. > >The reason that memset() was used here, is that there aren't many other ways >to get node_order zeroed, given that it is a statically defined variable. > > >> while ((node = find_next_best_node(local_node, &used_mask)) >= 0) { >> /* >> * We don't want to pressure a particular node. >> > > > >thanks, >-- >John Hubbard >NVIDIA -- Wei Yang Help you, Help me