lkml.org 
[lkml]   [2023]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes
    From
    On 14.02.23 12:26, Qi Zheng wrote:
    >
    >
    > 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?

    I still haven't figured out what we want to achieve with NODE_MIN_SIZE
    at all. It smells like an arch-specific hack looking at

    "Don't confuse VM with a node that doesn't have the minimum amount of
    memory"

    Why shouldn't mm-core deal with that?

    I'd appreciate an explanation of the bigger picture, what the issue is
    and what the approach to solve it is (including memory onlining/offlining).

    --
    Thanks,

    David / dhildenb

    \
     
     \ /
      Last update: 2023-03-27 00:21    [W:4.502 / U:0.116 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site