Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes

[Vlastimil Babka]

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@xxxxxxxxxxxxx>
>>> Reported-by: Teng Hu <huteng.ht@xxxxxxxxxxxxx>
>> 
>> 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.
> 
>> 
>>> ---
>>>   mm/page_alloc.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 588555754601..b9cce56f4e21 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -4188,6 +4188,11 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
>>>   			(alloc_flags & ALLOC_CPUSET) &&
>>>   			!__cpuset_zone_allowed(zone, gfp_mask))
>>>   				continue;
>>> +
>>> +		/* Don't allocate page from memoryless nodes. */
>>> +		if (!node_state((zone_to_nid(zone)), N_MEMORY))
>>> +			continue;
>>> +
>>>   		/*
>>>   		 * When allocating a page cache page for writing, we
>>>   		 * want to get it from a node that is within its dirty
>> 
>