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[142.68.57.212]) by smtp.gmail.com with ESMTPSA id 2sm5687986qtp.33.2020.03.27.16.18.20 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 27 Mar 2020 16:18:21 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1jHyF2-0002A1-HW; Fri, 27 Mar 2020 20:18:20 -0300 Date: Fri, 27 Mar 2020 20:18:20 -0300 From: Jason Gunthorpe To: John Hubbard Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@redhat.com Subject: Re: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero Message-ID: <20200327231820.GA20941@ziepe.ca> 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: Mutt/1.9.4 (2018-02-28) 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 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 > > +++ 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... It is also redundant, all static data is 0 initialized in Linux and should not be explicitly initialized so it can remain in .bss > > @@ -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. Indeed Jason