Re: [PATCH v3 0/5] Make cpuid <-> nodeid mapping persistent.

[Yasuaki Ishimatsu]

Hi Tang,

I applied your patches into linux-4.4.0-rc4 and tried to boot up
the system with mem= boot option, but system does not boot up.
Unfortunately boot messages were not shown. So I cannot find out
the reason.

The reason of using the mem= boot option is to limit memory and
create memoryless node on purpose since your patches support
memoryless node.

Here is an example method to create memoryless node on purpose.

My box has the following SRAT:

SRAT: Node 0 PXM 0 [mem 0x00000000-0x5fffffff]
SRAT: Node 0 PXM 0 [mem 0x100000000-0x109fffffff]
SRAT: Node 1 PXM 1 [mem 0x10a0000000-0x209fffffff]
SRAT: Node 2 PXM 2 [mem 0x20a0000000-0x309fffffff]
SRAT: Node 3 PXM 3 [mem 0x30a0000000-0x409fffffff]

So when booting up the system with mem=0x20a0000000, Memory of
Node 2 and 3 are ignored and the Nodes become memoryless node.

Thanks,
Yasuaki Ishimatsu
On Thu, 19 Nov 2015 12:22:10 +0800
Tang Chen <tangchen@xxxxxxxxxxxxxx> wrote:

> [Problem]
> 
> cpuid <-> nodeid mapping is firstly established at boot time. And workqueue caches
> the mapping in wq_numa_possible_cpumask in wq_numa_init() at boot time.
> 
> When doing node online/offline, cpuid <-> nodeid mapping is established/destroyed,
> which means, cpuid <-> nodeid mapping will change if node hotplug happens. But
> workqueue does not update wq_numa_possible_cpumask.
> 
> So here is the problem:
> 
> Assume we have the following cpuid <-> nodeid in the beginning:
> 
>   Node | CPU
> ------------------------
> node 0 |  0-14, 60-74
> node 1 | 15-29, 75-89
> node 2 | 30-44, 90-104
> node 3 | 45-59, 105-119
> 
> and we hot-remove node2 and node3, it becomes:
> 
>   Node | CPU
> ------------------------
> node 0 |  0-14, 60-74
> node 1 | 15-29, 75-89
> 
> and we hot-add node4 and node5, it becomes:
> 
>   Node | CPU
> ------------------------
> node 0 |  0-14, 60-74
> node 1 | 15-29, 75-89
> node 4 | 30-59
> node 5 | 90-119
> 
> But in wq_numa_possible_cpumask, cpu30 is still mapped to node2, and the like.
> 
> When a pool workqueue is initialized, if its cpumask belongs to a node, its
> pool->node will be mapped to that node. And memory used by this workqueue will
> also be allocated on that node.
> 
> static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs){
> ...
>         /* if cpumask is contained inside a NUMA node, we belong to that node */
>         if (wq_numa_enabled) {
>                 for_each_node(node) {
>                         if (cpumask_subset(pool->attrs->cpumask,
>                                            wq_numa_possible_cpumask[node])) {
>                                 pool->node = node;
>                                 break;
>                         }
>                 }
>         }
> 
> Since wq_numa_possible_cpumask is not updated, it could be mapped to an offline node,
> which will lead to memory allocation failure:
> 
>  SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
>   cache: kmalloc-192, object size: 192, buffer size: 192, default order: 1, min order: 0
>   node 0: slabs: 6172, objs: 259224, free: 245741
>   node 1: slabs: 3261, objs: 136962, free: 127656
> 
> It happens here:
> 
> create_worker(struct worker_pool *pool)
>  |--> worker = alloc_worker(pool->node);
> 
> static struct worker *alloc_worker(int node)
> {
>         struct worker *worker;
> 
>         worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node); --> Here, useing the wrong node.
> 
>         ......
> 
>         return worker;
> }
> 
> 
> [Solution]
> 
> There are four mappings in the kernel:
> 1. nodeid (logical node id)   <->   pxm
> 2. apicid (physical cpu id)   <->   nodeid
> 3. cpuid (logical cpu id)     <->   apicid
> 4. cpuid (logical cpu id)     <->   nodeid
> 
> 1. pxm (proximity domain) is provided by ACPI firmware in SRAT, and nodeid <-> pxm
>    mapping is setup at boot time. This mapping is persistent, won't change.
> 
> 2. apicid <-> nodeid mapping is setup using info in 1. The mapping is setup at boot
>    time and CPU hotadd time, and cleared at CPU hotremove time. This mapping is also
>    persistent.
> 
> 3. cpuid <-> apicid mapping is setup at boot time and CPU hotadd time. cpuid is
>    allocated, lower ids first, and released at CPU hotremove time, reused for other
>    hotadded CPUs. So this mapping is not persistent.
> 
> 4. cpuid <-> nodeid mapping is also setup at boot time and CPU hotadd time, and
>    cleared at CPU hotremove time. As a result of 3, this mapping is not persistent.
> 
> To fix this problem, we establish cpuid <-> nodeid mapping for all the possible
> cpus at boot time, and make it persistent. And according to init_cpu_to_node(),
> cpuid <-> nodeid mapping is based on apicid <-> nodeid mapping and cpuid <-> apicid
> mapping. So the key point is obtaining all cpus' apicid.
> 
> apicid can be obtained by _MAT (Multiple APIC Table Entry) method or found in
> MADT (Multiple APIC Description Table). So we finish the job in the following steps:
> 
> 1. Enable apic registeration flow to handle both enabled and disabled cpus.
>    This is done by introducing an extra parameter to generic_processor_info to let the
>    caller control if disabled cpus are ignored.
> 
> 2. Introduce a new array storing all possible cpuid <-> apicid mapping. And also modify
>    the way cpuid is calculated. Establish all possible cpuid <-> apicid mapping when
>    registering local apic. Store the mapping in this array.
> 
> 3. Enable _MAT and MADT relative apis to return non-presnet or disabled cpus' apicid.
>    This is also done by introducing an extra parameter to these apis to let the caller
>    control if disabled cpus are ignored.
> 
> 4. Establish all possible cpuid <-> nodeid mapping.
>    This is done via an additional acpi namespace walk for processors.
> 
> 
> For previous discussion, please refer to:
> https://lkml.org/lkml/2015/2/27/145
> https://lkml.org/lkml/2015/3/25/989
> https://lkml.org/lkml/2015/5/14/244
> https://lkml.org/lkml/2015/7/7/200
> https://lkml.org/lkml/2015/9/27/209
> 
> 
> Change log v2 -> v3:
> 1. Online memory-less nodes at boot time to map cpus of memory-less nodes.
> 2. Build zonelists for memory-less nodes so that memory allocator will fall 
>    back to proper nodes automatically.
> 
> Change log v1 -> v2:
> 1. Split code movement and actual changes. Add patch 1.
> 2. Synchronize best near online node record when node hotplug happens. In patch 2.
> 3. Fix some comment.
> 
> 
> Gu Zheng (4):
>   x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at
>     boot time.
>   x86, acpi, cpu-hotplug: Introduce cpuid_to_apicid[] array to store
>     persistent cpuid <-> apicid mapping.
>   x86, acpi, cpu-hotplug: Enable MADT APIs to return disabled apicid.
>   x86, acpi, cpu-hotplug: Set persistent cpuid <-> nodeid mapping when
>     booting.
> 
> Tang Chen (1):
>   x86, memhp, numa: Online memory-less nodes at boot time.
> 
>  arch/ia64/kernel/acpi.c       |   2 +-
>  arch/x86/include/asm/mpspec.h |   1 +
>  arch/x86/kernel/acpi/boot.c   |   8 ++-
>  arch/x86/kernel/apic/apic.c   |  85 +++++++++++++++++++++++++----
>  arch/x86/mm/numa.c            |  30 ++++++-----
>  drivers/acpi/acpi_processor.c |   5 +-
>  drivers/acpi/bus.c            |   3 ++
>  drivers/acpi/processor_core.c | 122 ++++++++++++++++++++++++++++++++++--------
>  include/linux/acpi.h          |   2 +
>  include/linux/mmzone.h        |   1 +
>  mm/page_alloc.c               |   2 +-
>  11 files changed, 209 insertions(+), 52 deletions(-)
> 
> -- 
> 1.8.3.1
> 
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