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[79.242.62.87]) by smtp.gmail.com with ESMTPSA id f7sm3775406wmg.6.2021.12.07.07.34.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Dec 2021 07:34:31 -0800 (PST) Message-ID: Date: Tue, 7 Dec 2021 16:34:30 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages Content-Language: en-US To: Michal Hocko Cc: Alexey Makhalov , Dennis Zhou , Eric Dumazet , "linux-mm@kvack.org" , Andrew Morton , Oscar Salvador , Tejun Heo , Christoph Lameter , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" References: <5239D699-523C-4F0C-923A-B068E476043E@vmware.com> <1043a1a4-b7f2-8730-d192-7cab9f15ee24@redhat.com> <77e785e6-cf34-0cff-26a5-852d3786a9b8@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.12.21 16:29, Michal Hocko wrote: > On Tue 07-12-21 16:09:39, David Hildenbrand wrote: >> On 07.12.21 14:23, Michal Hocko wrote: >>> On Tue 07-12-21 13:28:31, David Hildenbrand wrote: >>> [...] >>>> But maybe I am missing something important regarding online vs. offline >>>> nodes that your patch changes? >>> >>> I am relying on alloc_node_data setting the node online. But if we are >>> to change the call to arch_alloc_node_data then the patch needs to be >>> more involved. Here is what I have right now. If this happens to be the >>> right way then there is some additional work to sync up with the hotplug >>> code. >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index c5952749ad40..a296e934ad2f 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -8032,8 +8032,23 @@ void __init free_area_init(unsigned long *max_zone_pfn) >>> /* Initialise every node */ >>> mminit_verify_pageflags_layout(); >>> setup_nr_node_ids(); >>> - for_each_online_node(nid) { >>> - pg_data_t *pgdat = NODE_DATA(nid); >>> + for_each_node(nid) { >>> + pg_data_t *pgdat; >>> + >>> + if (!node_online(nid)) { >>> + pr_warn("Node %d uninitialized by the platform. Please report with memory map.\n", nid); >>> + pgdat = arch_alloc_nodedata(nid); >>> + pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat); >>> + arch_refresh_nodedata(nid, pgdat); >>> + node_set_online(nid); >> >> Setting all possible nodes online might result in quite some QE noice, >> because all these nodes will then be visible in the sysfs and >> try_offline_nodes() is essentially for the trash. > > I am not sure I follow. I believe sysfs will not get populate because I > do not call register_one_node. arch/x86/kernel/topology.c:topology_init() for_each_online_node(i) register_one_node(i); > > You are right that try_offline_nodes will be reduce which is good imho. > More changes will be possible (hopefully to drop some ugly code) on top > of this change (or any other that achieves that there are no NULL pgdat > for possible nodes). > No to exposing actually offline nodes to user space via sysfs. Let's concentrate on preallocating the pgdat and fixing the issue at hand. One step at a time please. >> I agree to prealloc the pgdat, I don't think we should actually set the >> nodes online. Node onlining/offlining should be done when we do have >> actual CPUs/memory populated. > > If we keep the offline/online node state notion we are not solving an > important aspect of the problem - confusing api. I don't think it's that confusing. Just like we do have online and offline CPUs. Or online and offline memory blocks. Similarly, a node is either online or offline. -- Thanks, David / dhildenb