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 3AFE36B6DCA for ; Tue, 4 Dec 2018 03:40:55 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id s50so7806628edd.11 for ; Tue, 04 Dec 2018 00:40:55 -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 l37sor8889057edb.2.2018.12.04.00.40.53 for (Google Transport Security); Tue, 04 Dec 2018 00:40:53 -0800 (PST) Date: Tue, 4 Dec 2018 08:40:52 +0000 From: Wei Yang Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline Message-ID: <20181204084052.gpwwlnp6n2zehjy5@master> Reply-To: Wei Yang References: <1543892757-4323-1-git-send-email-kernelfans@gmail.com> <20181204072251.GT31738@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Pingfan Liu Cc: mhocko@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Mike Rapoport , Bjorn Helgaas , Jonathan Cameron On Tue, Dec 04, 2018 at 04:20:32PM +0800, Pingfan Liu wrote: >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. If my understanding is correct, we can't do page alloc before zonelist is initialized. I guess Michal's point is to figure out this reason. > >> 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 -- Wei Yang Help you, Help me