[PATCH v2] powerpc/nvdimm: Pick the nearby online node if the device node is not online
Aneesh Kumar K.V
aneesh.kumar at linux.ibm.com
Thu Jul 18 17:49:20 AEST 2019
"Oliver O'Halloran" <oohall at gmail.com> writes:
> On Tue, Jul 16, 2019 at 7:08 PM Aneesh Kumar K.V
> <aneesh.kumar at linux.ibm.com> wrote:
>>
>> This is similar to what ACPI does. Nvdimm layer doesn't bring the SCM device
>> numa node online. Hence we need to make sure we always use an online node
>> as ndr_desc.numa_node. Otherwise this result in kernel crashes. The target
>> node is used by dax/kmem and that will bring up the numa node online correctly.
>>
>> Without this patch, we do hit kernel crash as below because we try to access
>> uninitialized NODE_DATA in different code paths.
>
> Right, so we're getting a crash due to libnvdimm (via devm_kmalloc)
> trying to to node local allocations to an offline node. Using a
> different node fixes that problem, but what else does changing
> ndr_desc.numa_node do?
>
>> cpu 0x0: Vector: 300 (Data Access) at [c0000000fac53170]
>> pc: c0000000004bbc50: ___slab_alloc+0x120/0xca0
>> lr: c0000000004bc834: __slab_alloc+0x64/0xc0
>> sp: c0000000fac53400
>> msr: 8000000002009033
>> dar: 73e8
>> dsisr: 80000
>> current = 0xc0000000fabb6d80
>> paca = 0xc000000003870000 irqmask: 0x03 irq_happened: 0x01
>> pid = 7, comm = kworker/u16:0
>> Linux version 5.2.0-06234-g76bd729b2644 (kvaneesh at ltc-boston123) (gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)) #135 SMP Thu Jul 11 05:36:30 CDT 2019
>> enter ? for help
>> [link register ] c0000000004bc834 __slab_alloc+0x64/0xc0
>> [c0000000fac53400] c0000000fac53480 (unreliable)
>> [c0000000fac53500] c0000000004bc818 __slab_alloc+0x48/0xc0
>> [c0000000fac53560] c0000000004c30a0 __kmalloc_node_track_caller+0x3c0/0x6b0
>> [c0000000fac535d0] c000000000cfafe4 devm_kmalloc+0x74/0xc0
>> [c0000000fac53600] c000000000d69434 nd_region_activate+0x144/0x560
>> [c0000000fac536d0] c000000000d6b19c nd_region_probe+0x17c/0x370
>> [c0000000fac537b0] c000000000d6349c nvdimm_bus_probe+0x10c/0x230
>> [c0000000fac53840] c000000000cf3cc4 really_probe+0x254/0x4e0
>> [c0000000fac538d0] c000000000cf429c driver_probe_device+0x16c/0x1e0
>> [c0000000fac53950] c000000000cf0b44 bus_for_each_drv+0x94/0x130
>> [c0000000fac539b0] c000000000cf392c __device_attach+0xdc/0x200
>> [c0000000fac53a50] c000000000cf231c bus_probe_device+0x4c/0xf0
>> [c0000000fac53a90] c000000000ced268 device_add+0x528/0x810
>> [c0000000fac53b60] c000000000d62a58 nd_async_device_register+0x28/0xa0
>> [c0000000fac53bd0] c0000000001ccb8c async_run_entry_fn+0xcc/0x1f0
>> [c0000000fac53c50] c0000000001bcd9c process_one_work+0x46c/0x860
>> [c0000000fac53d20] c0000000001bd4f4 worker_thread+0x364/0x5f0
>> [c0000000fac53db0] c0000000001c7260 kthread+0x1b0/0x1c0
>> [c0000000fac53e20] c00000000000b954 ret_from_kernel_thread+0x5c/0x68
>>
>> With the patch we get
>>
>> # numactl -H
>> available: 2 nodes (0-1)
>> node 0 cpus:
>> node 0 size: 0 MB
>> node 0 free: 0 MB
>> node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
>> node 1 size: 130865 MB
>> node 1 free: 129130 MB
>> node distances:
>> node 0 1
>> 0: 10 20
>> 1: 20 10
>> # cat /sys/bus/nd/devices/region0/numa_node
>> 0
>> # dmesg | grep papr_scm
>> [ 91.332305] papr_scm ibm,persistent-memory:ibm,pmemory at 44104001: Region registered with target node 2 and online node 0
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>> ---
>> changes from V1:
>> * handle NUMA_NO_NODE
>>
>> arch/powerpc/platforms/pseries/papr_scm.c | 30 +++++++++++++++++++++--
>> 1 file changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>> index c8ec670ee924..b813bc92f35f 100644
>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>> @@ -255,12 +255,32 @@ static const struct attribute_group *papr_scm_dimm_groups[] = {
>> NULL,
>> };
>>
>> +static inline int papr_scm_node(int node)
>> +{
>> + int min_dist = INT_MAX, dist;
>> + int nid, min_node;
>> +
>> + if ((node == NUMA_NO_NODE) || node_online(node))
>> + return node;
>> +
>> + min_node = first_online_node;
>> + for_each_online_node(nid) {
>> + dist = node_distance(node, nid);
>> + if (dist < min_dist) {
>> + min_dist = dist;
>> + min_node = nid;
>> + }
>> + }
>> + return min_node;
>> +}
>> +
>> static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>> {
>> struct device *dev = &p->pdev->dev;
>> struct nd_mapping_desc mapping;
>> struct nd_region_desc ndr_desc;
>> unsigned long dimm_flags;
>> + int target_nid, online_nid;
>>
>> p->bus_desc.ndctl = papr_scm_ndctl;
>> p->bus_desc.module = THIS_MODULE;
>> @@ -299,8 +319,11 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>
>> memset(&ndr_desc, 0, sizeof(ndr_desc));
>> ndr_desc.attr_groups = region_attr_groups;
>> - ndr_desc.numa_node = dev_to_node(&p->pdev->dev);
>> - ndr_desc.target_node = ndr_desc.numa_node;
>> + target_nid = dev_to_node(&p->pdev->dev);
>> + online_nid = papr_scm_node(target_nid);
>> + set_dev_node(&p->pdev->dev, online_nid);
>> + ndr_desc.numa_node = online_nid;
>> + ndr_desc.target_node = target_nid;
>
> Annoying question: Say I have two SCM regions with slightly different
> numa affinities and I online one, then the other. If the first is
> setup to be used as kmem could we have the target_node of the first
> being used as the online_node of the second? If so, what happens if I
> unbind kmem from the first region?
kmem, for now, doesn't allow to unregister the mem region. So this won't
happen. But when we start supporting hot unplugging memory added via
kmem, I would expect we continue to keep the SCM region 1 attached to
the node that had kmem before.
>
> I'm mostly wondering if we need to set online_node to the nearest node
> with actual memory on it.
>
>> ndr_desc.res = &p->res;
>> ndr_desc.of_node = p->dn;
>> ndr_desc.provider_data = p;
>> @@ -318,6 +341,9 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>> ndr_desc.res, p->dn);
>> goto err;
>> }
>> + if (target_nid != online_nid)
>> + dev_info(dev, "Region registered with target node %d and online node %d",
>> + target_nid, online_nid);
>>
>> return 0;
>>
There was a related question that Michael asked w.r.t how do we
define closest NUMA node if we have two NUMA nodes (say `x` and `y`)
with the same distance from the nvdimm region NUMA node. For now, we
pick the first one. But then that also means we lose the information
that nvdimm region access latency is going to be same from both nodes
`x` and `y`.
I guess if application want to find those detail, they will have to use
/sys/devices/system/node/nodeX/accessY/ introduced as part of
08d9dbe72b1f8 ("node: Link memory nodes to their compute nodes")
-aneesh
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