Re: [PATCH RESEND] mm: hugetlb: simplify per-node sysfs creation and removal

David Hildenbrand
2022-08-23T15:12:40Z

On 19.08.22 10:00, Muchun Song wrote:
> The following commit offload per-node sysfs creation and removal to a kworker and
> did not say why it is needed. And it also said "I don't know that this is
> absolutely required". It seems like the author was not sure as well. Since it
> only complicates the code, this patch will revert the changes to simplify the code.
>
> 39da08cb074c ("hugetlb: offload per node attribute registrations")
>
> We could use memory hotplug notifier to do per-node sysfs creation and removal
> instead of inserting those operations to node registration and unregistration.
> Then, it can reduce the code coupling between node.c and hugetlb.c. Also, it can
> simplify the code.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

[...]

> @@ -683,7 +626,6 @@ static int register_node(struct node *node, int num)
> void unregister_node(struct node *node)
> {
> compaction_unregister_node(node);
> - hugetlb_unregister_node(node); /* no-op, if memoryless node */
> node_remove_accesses(node);
> node_remove_caches(node);
> device_unregister(&node->dev);
> @@ -905,74 +847,8 @@ void register_memory_blocks_under_node(int nid, unsigned long start_pfn,
> (void *)&nid, func);
> return;
> }

[...]

> /*
> * Create all node devices, which will properly link the node
> * to applicable memory block devices and already created cpu devices.
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 40d641a8bfb0..ea817b507f54 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -2,15 +2,15 @@
> /*
> * include/linux/node.h - generic node definition
> *
> - * This is mainly for topological representation. We define the
> - * basic 'struct node' here, which can be embedded in per-arch
> + * This is mainly for topological representation. We define the
> + * basic 'struct node' here, which can be embedded in per-arch
> * definitions of processors.
> *
> * Basic handling of the devices is done in drivers/base/node.c
> - * and system devices are handled in drivers/base/sys.c.
> + * and system devices are handled in drivers/base/sys.c.
> *
> * Nodes are exported via driverfs in the class/node/devices/
> - * directory.
> + * directory.

Unrelated changes.

> */
> #ifndef _LINUX_NODE_H_
> #define _LINUX_NODE_H_
> @@ -18,7 +18,6 @@
> #include <linux/device.h>
> #include <linux/cpumask.h>
> #include <linux/list.h>
> -#include <linux/workqueue.h>
>
> /**
> * struct node_hmem_attrs - heterogeneous memory performance attributes
> @@ -84,10 +83,6 @@ static inline void node_set_perf_attrs(unsigned int nid,
> struct node {
> struct device dev;
> struct list_head access_list;
> -
> -#if defined(CONFIG_MEMORY_HOTPLUG) && defined(CONFIG_HUGETLBFS)
> - struct work_struct node_work;
> -#endif
> #ifdef CONFIG_HMEM_REPORTING
> struct list_head cache_attrs;
> struct device *cache_dev;
> @@ -96,7 +91,6 @@ struct node {
>
> struct memory_block;
> extern struct node *node_devices[];
> -typedef void (*node_registration_func_t)(struct node *);
>
> #if defined(CONFIG_MEMORY_HOTPLUG) && defined(CONFIG_NUMA)
> void register_memory_blocks_under_node(int nid, unsigned long start_pfn,
> @@ -144,11 +138,6 @@ extern void unregister_memory_block_under_nodes(struct memory_block *mem_blk);
> extern int register_memory_node_under_compute_node(unsigned int mem_nid,
> unsigned int cpu_nid,
> unsigned access);
> -
> -#ifdef CONFIG_HUGETLBFS
> -extern void register_hugetlbfs_with_node(node_registration_func_t doregister,
> - node_registration_func_t unregister);
> -#endif
> #else
> static inline void node_dev_init(void)
> {
> @@ -176,11 +165,6 @@ static inline int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
> static inline void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> {
> }
> -
> -static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
> - node_registration_func_t unreg)
> -{
> -}
> #endif
>
> #define to_node(device) container_of(device, struct node, dev)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 536a52c29035..9a72499486c1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -33,6 +33,7 @@
> #include <linux/migrate.h>
> #include <linux/nospec.h>
> #include <linux/delayacct.h>
> +#include <linux/memory.h>
>
> #include <asm/page.h>
> #include <asm/pgalloc.h>
> @@ -3967,19 +3968,19 @@ static void hugetlb_unregister_node(struct node *node)
> * Register hstate attributes for a single node device.
> * No-op if attributes already registered.
> */
> -static void hugetlb_register_node(struct node *node)
> +static int hugetlb_register_node(struct node *node)
> {
> struct hstate *h;
> struct node_hstate *nhs = &node_hstates[node->dev.id];
> int err;
>
> if (nhs->hugepages_kobj)
> - return; /* already allocated */
> + return 0; /* already allocated */
>
> nhs->hugepages_kobj = kobject_create_and_add("hugepages",
> &node->dev.kobj);
> if (!nhs->hugepages_kobj)
> - return;
> + return -ENOMEM;
>
> for_each_hstate(h) {
> err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
> @@ -3989,9 +3990,28 @@ static void hugetlb_register_node(struct node *node)
> pr_err("HugeTLB: Unable to add hstate %s for node %d\n",
> h->name, node->dev.id);
> hugetlb_unregister_node(node);
> - break;
> + return -ENOMEM;
> }
> }
> + return 0;
> +}
> +
> +static int __meminit hugetlb_memory_callback(struct notifier_block *self,
> + unsigned long action, void *arg)
> +{
> + int ret = 0;
> + struct memory_notify *mnb = arg;
> + int nid = mnb->status_change_nid;
> +
> + if (nid == NUMA_NO_NODE)
> + return NOTIFY_DONE;
> +
> + if (action == MEM_GOING_ONLINE)
> + ret = hugetlb_register_node(node_devices[nid]);
> + else if (action == MEM_CANCEL_ONLINE || action == MEM_OFFLINE)
> + hugetlb_unregister_node(node_devices[nid]);
> +
> + return notifier_from_errno(ret);
> }
>
> /*
> @@ -4003,18 +4023,11 @@ static void __init hugetlb_register_all_nodes(void)
> {
> int nid;
>
> - for_each_node_state(nid, N_MEMORY) {
> - struct node *node = node_devices[nid];
> - if (node->dev.id == nid)
> - hugetlb_register_node(node);
> - }
> -
> - /*
> - * Let the node device driver know we're here so it can
> - * [un]register hstate attributes on node hotplug.
> - */
> - register_hugetlbfs_with_node(hugetlb_register_node,
> - hugetlb_unregister_node);
> + get_online_mems();
> + hotplug_memory_notifier(hugetlb_memory_callback, 0);
> + for_each_node_state(nid, N_MEMORY)
> + hugetlb_register_node(node_devices[nid]);
> + put_online_mems();
> }
> #else /* !CONFIG_NUMA */

Do we really *need* the memory hotplug notifier and the added complexity
due for handling memory-less nodes?

Why can't we simply register/unregister sysfs entries in
register_node/unregister_node and call it a day?

TBH, we should just have sysfs entries for memory-less nodes and not
care about such (corner) cases.

--
Thanks,

David / dhildenb