From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id D55646B6DAD for ; Tue, 4 Dec 2018 03:20:45 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id m19so7883765edc.6 for ; Tue, 04 Dec 2018 00:20:45 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id e28sor8756064edb.24.2018.12.04.00.20.44 for (Google Transport Security); Tue, 04 Dec 2018 00:20:44 -0800 (PST) MIME-Version: 1.0 References: <1543892757-4323-1-git-send-email-kernelfans@gmail.com> <20181204072251.GT31738@dhcp22.suse.cz> In-Reply-To: <20181204072251.GT31738@dhcp22.suse.cz> From: Pingfan Liu Date: Tue, 4 Dec 2018 16:20:32 +0800 Message-ID: Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Mike Rapoport , Bjorn Helgaas , Jonathan Cameron On Tue, Dec 4, 2018 at 3:22 PM Michal Hocko wrote: > > On Tue 04-12-18 11:05:57, Pingfan Liu wrote: > > During my test on some AMD machine, with kexec -l nr_cpus=x option, the > > kernel failed to bootup, because some node's data struct can not be allocated, > > e.g, on x86, initialized by init_cpu_to_node()->init_memory_less_node(). But > > device->numa_node info is used as preferred_nid param for > > __alloc_pages_nodemask(), which causes NULL reference > > ac->zonelist = node_zonelist(preferred_nid, gfp_mask); > > This patch tries to fix the issue by falling back to the first online node, > > when encountering such corner case. > > We have seen similar issues already and the bug was usually that the > zonelists were not initialized yet or the node is completely bogus. > Zonelists should be initialized by build_all_zonelists quite early so I > am wondering whether the later is the case. What is the actual node > number the device is associated with? > The device's node num is 2. And in my case, I used nr_cpus param. Due to init_cpu_to_node() initialize all the possible node. It is hard for me to figure out without this param, how zonelists is accessed before page allocator works. > Your patch is not correct btw, because we want to fallback into the node in > the distance order rather into the first online node. > -- What about this: +extern int find_next_best_node(int node, nodemask_t *used_node_mask); + /* * We get the zone list from the current node and the gfp_mask. * This zone list contains a maximum of MAXNODES*MAX_NR_ZONES zones. @@ -453,6 +455,11 @@ static inline int gfp_zonelist(gfp_t flags) */ static inline struct zonelist *node_zonelist(int nid, gfp_t flags) { + if (unlikely(!node_online(nid))) { + nodemask_t used_mask; + nodes_complement(used_mask, node_online_map); + nid = find_next_best_node(nid, &used_mask); + } return NODE_DATA(nid)->node_zonelists + gfp_zonelist(flags); } I just finished the compiling, not test it yet, since the machine is not on hand yet. It needs some time to get it again. Thanks, Pingfan