Re: [PATCH v2 0/7] Make cpuid <-> nodeid mapping persistent.

[Yasuaki Ishimatsu]

Hi Tang,

Your patch assumes that system supports memory less node and
fixes the issue on x86 architecture.

But if system does not supports memory less node, your patch cannot
fix the issue. It means that system must support memory less node
to support Node (CPU and memory) hotplug.

Why don't you fix workqueue directly?

Thanks,
Yasuaki Ishimatsu

On Thu, 10 Sep 2015 12:27:42 +0800
Tang Chen <tangchen@xxxxxxxxxxxxxx> wrote:

> The whole patch-set aims at solving this problem:
> 
> [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.
> 
> 
> Patch 1 ~ 3 are some prepare works.
> Patch 4 ~ 7 finishes the 4 steps above.
> 
> 
> 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
> 
> 
> 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 (5):
>   x86, gfp: Cache best near node for memory allocation.
>   x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at
>     boot time.
>   x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] 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 (2):
>   x86, numa: Move definition of find_near_online_node() forward.
>   x86, numa: Introduce a node to node array to map a node to its best
>     online node.
> 
>  arch/ia64/kernel/acpi.c         |   2 +-
>  arch/x86/include/asm/mpspec.h   |   1 +
>  arch/x86/include/asm/topology.h |  10 ++++
>  arch/x86/kernel/acpi/boot.c     |   8 +--
>  arch/x86/kernel/apic/apic.c     |  77 ++++++++++++++++++++++---
>  arch/x86/mm/numa.c              |  80 +++++++++++++++++++-------
>  drivers/acpi/acpi_processor.c   |   5 +-
>  drivers/acpi/bus.c              |   3 +
>  drivers/acpi/processor_core.c   | 122 +++++++++++++++++++++++++++++++++-------
>  include/linux/acpi.h            |   2 +
>  include/linux/gfp.h             |   8 ++-
>  mm/memory_hotplug.c             |   4 ++
>  12 files changed, 264 insertions(+), 58 deletions(-)
> 
> -- 
> 1.9.3
> 
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