From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 718BF6B6DD8 for ; Tue, 4 Dec 2018 03:56:04 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id y35so7939474edb.5 for ; Tue, 04 Dec 2018 00:56:04 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id t22-v6si336088ejl.294.2018.12.04.00.56.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 04 Dec 2018 00:56:03 -0800 (PST) Date: Tue, 4 Dec 2018 09:56:01 +0100 From: Michal Hocko Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline Message-ID: <20181204085601.GC1286@dhcp22.suse.cz> 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: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Mike Rapoport , Bjorn Helgaas , Jonathan Cameron On Tue 04-12-18 16:20:32, 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. I believe we should focus on this. Why does the node have no zonelist even though all zonelists should be initialized already? Maybe this is nr_cpus pecularity and we do not initialize all the existing numa nodes. Or maybe the device is associated to a non-existing node with that setup. A full dmesg might help us here. > > 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. This is clearly a no-go. nodemask_t can be giant and you cannot have it on the stack for allocation paths which might be called from a deep stack already. Also this is called from the allocator hot paths and each branch counts. -- Michal Hocko SUSE Labs