On Thu, Mar 17, 2016 at 2:31 AM, Zhu Guihua <zhugh.fnst@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 v5 -> v6:
> 1. Define func acpi_map_cpu2node() for x86 and ia64 respectively.
>
> Change log v4 -> v5:
> 1. Remove useless code in patch 1.
> 2. Small improvement of commit message.
>
> Change log v3 -> v4:
> 1. Fix the kernel panic at boot time. The cause is that I tried to build zonelists
> before per cpu areas were initialized.
>
> 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 | 27 +++++-----
> drivers/acpi/acpi_processor.c | 5 +-
> drivers/acpi/bus.c | 3 ++
> drivers/acpi/processor_core.c | 122 ++++++++++++++++++++++++++++++++++--------
> include/linux/acpi.h | 6 +++
> 9 files changed, 208 insertions(+), 51 deletions(-)
>
OK
Since I know that there is demand for these changes, I'll queue them
up early for 4.7 if there are no comments from the x86 maintainers
till then.
Thanks,
Rafael
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