Messages in this thread | | | Date | Tue, 14 Feb 2023 19:26:23 +0800 | Subject | Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes | From | Qi Zheng <> |
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On 2023/2/14 19:22, David Hildenbrand wrote: > On 14.02.23 11:26, Qi Zheng wrote: >> >> >> On 2023/2/14 17:43, Mike Rapoport wrote: >>> On Tue, Feb 14, 2023 at 10:17:03AM +0100, David Hildenbrand wrote: >>>> On 14.02.23 09:42, Vlastimil Babka wrote: >>>>> On 2/13/23 12:00, Qi Zheng wrote: >>>>>> >>>>>> >>>>>> On 2023/2/13 16:47, Vlastimil Babka wrote: >>>>>>> On 2/12/23 12:03, Qi Zheng wrote: >>>>>>>> In x86, numa_register_memblks() is only interested in >>>>>>>> those nodes which have enough memory, so it skips over >>>>>>>> all nodes with memory below NODE_MIN_SIZE (treated as >>>>>>>> a memoryless node). Later on, we will initialize these >>>>>>>> memoryless nodes (allocate pgdat in free_area_init() >>>>>>>> and build zonelist etc), and will online these nodes >>>>>>>> in init_cpu_to_node() and init_gi_nodes(). >>>>>>>> >>>>>>>> After boot, these memoryless nodes are in N_ONLINE >>>>>>>> state but not in N_MEMORY state. But we can still allocate >>>>>>>> pages from these memoryless nodes. >>>>>>>> >>>>>>>> In SLUB, we only process nodes in the N_MEMORY state, >>>>>>>> such as allocating their struct kmem_cache_node. So if >>>>>>>> we allocate a page from the memoryless node above to >>>>>>>> SLUB, the struct kmem_cache_node of the node corresponding >>>>>>>> to this page is NULL, which will cause panic. >>>>>>>> >>>>>>>> For example, if we use qemu to start a two numa node kernel, >>>>>>>> one of the nodes has 2M memory (less than NODE_MIN_SIZE), >>>>>>>> and the other node has 2G, then we will encounter the >>>>>>>> following panic: >>>>>>>> >>>>>>>> [ 0.149844] BUG: kernel NULL pointer dereference, address: >>>>>>>> 0000000000000000 >>>>>>>> [ 0.150783] #PF: supervisor write access in kernel mode >>>>>>>> [ 0.151488] #PF: error_code(0x0002) - not-present page >>>>>>>> <...> >>>>>>>> [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 >>>>>>>> <...> >>>>>>>> [ 0.169781] Call Trace: >>>>>>>> [ 0.170159] <TASK> >>>>>>>> [ 0.170448] deactivate_slab+0x187/0x3c0 >>>>>>>> [ 0.171031] ? bootstrap+0x1b/0x10e >>>>>>>> [ 0.171559] ? preempt_count_sub+0x9/0xa0 >>>>>>>> [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 >>>>>>>> [ 0.172735] ? bootstrap+0x1b/0x10e >>>>>>>> [ 0.173236] bootstrap+0x6b/0x10e >>>>>>>> [ 0.173720] kmem_cache_init+0x10a/0x188 >>>>>>>> [ 0.174240] start_kernel+0x415/0x6ac >>>>>>>> [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb >>>>>>>> [ 0.175417] </TASK> >>>>>>>> [ 0.175713] Modules linked in: >>>>>>>> [ 0.176117] CR2: 0000000000000000 >>>>>>>> >>>>>>>> In addition, we can also encountered this panic in the actual >>>>>>>> production environment. We set up a 2c2g container with two >>>>>>>> numa nodes, and then reserved 128M for kdump, and then we >>>>>>>> can encountered the above panic in the kdump kernel. >>>>>>>> >>>>>>>> To fix it, we can filter memoryless nodes when allocating >>>>>>>> pages. >>>>>>>> >>>>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> >>>>>>>> Reported-by: Teng Hu <huteng.ht@bytedance.com> >>>>>>> >>>>>>> Well AFAIK the key mechanism to only allocate from "good" nodes >>>>>>> is the >>>>>>> zonelist, we shouldn't need to start putting extra checks like >>>>>>> this. So it >>>>>>> seems to me that the code building the zonelists should take the >>>>>>> NODE_MIN_SIZE constraint in mind. >>>>>> >>>>>> Indeed. How about the following patch: >>>>> >>>>> +Cc also David, forgot earlier. >>>>> >>>>> Looks good to me, at least. >>>>> >>>>>> @@ -6382,8 +6378,11 @@ int find_next_best_node(int node, nodemask_t >>>>>> *used_node_mask) >>>>>> int min_val = INT_MAX; >>>>>> int best_node = NUMA_NO_NODE; >>>>>> >>>>>> - /* Use the local node if we haven't already */ >>>>>> - if (!node_isset(node, *used_node_mask)) { >>>>>> + /* >>>>>> + * Use the local node if we haven't already. But for >>>>>> memoryless >>>>>> local >>>>>> + * node, we should skip it and fallback to other nodes. >>>>>> + */ >>>>>> + if (!node_isset(node, *used_node_mask) && node_state(node, >>>>>> N_MEMORY)) { >>>>>> node_set(node, *used_node_mask); >>>>>> return node; >>>>>> } >>>>>> >>>>>> For memoryless node, we skip it and fallback to other nodes when >>>>>> build its zonelists. >>>>>> >>>>>> Say we have node0 and node1, and node0 is memoryless, then: >>>>>> >>>>>> [ 0.102400] Fallback order for Node 0: 1 >>>>>> [ 0.102931] Fallback order for Node 1: 1 >>>>>> >>>>>> In this way, we will not allocate pages from memoryless node0. >>>>>> >>>> >>>> In offline_pages(), we'll first build_all_zonelists() to then >>>> node_states_clear_node()->node_clear_state(node, N_MEMORY); >>>> >>>> So at least on the offlining path, we wouldn't detect it properly yet I >>>> assume, and build a zonelist that contains a now-memory-less node? >>> >>> Another question is what happens if a new memory is plugged into a node >>> that had < NODE_MIN_SIZE of memory and after hotplug it stops being >>> "memoryless". >> >> When going online and offline a memory will re-call >> build_all_zonelists() to re-establish the zonelists (the zonelist of >> itself and other nodes). So it can stop being "memoryless" >> automatically. >> >> But in online_pages(), did not see the check of < NODE_MIN_SIZE. > > TBH, this is the first time I hear of NODE_MIN_SIZE and it seems to be a > pretty x86 specific thing. > > Are we sure we want to get NODE_MIN_SIZE involved?
Maybe add an arch_xxx() to handle it?
>
-- Thanks, Qi
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