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[79.242.62.87]) by smtp.gmail.com with ESMTPSA id q123sm2958207wma.30.2021.12.07.08.09.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Dec 2021 08:09:51 -0800 (PST) Message-ID: Date: Tue, 7 Dec 2021 17:09:50 +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 16:56, Michal Hocko wrote: > On Tue 07-12-21 16:34:30, David Hildenbrand wrote: >> 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); > > Right you are. > >>> 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. > > Why is that a problem with the sysfs for non-populated nodes? > https://lore.kernel.org/linuxppc-dev/20200428093836.27190-1-srikar@linux.vnet.ibm.com/t/ Contains some points -- certainly nothing unfixable but it clearly shows that users expect only nodes with actual memory and cpus to be online -- that's why we export the possible+online state to user space. My point is to be careful with such drastic changes and do one step at a time. I think preallocation of the pgdat is a reasonable thing to have without changing user-space visible semantics or even in-kernel semantics. -- Thanks, David / dhildenb