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Date: Thu, 1 Sep 2022 14:30:45 +0530
From: Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To: Muchun Song <songmuchun@...edance.com>, gregkh@...uxfoundation.org,
rafael@...nel.org, mike.kravetz@...cle.com,
akpm@...ux-foundation.org, osalvador@...e.de, david@...hat.com,
ying.huang@...el.com, rientjes@...gle.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: hugetlb: eliminate memory-less nodes handling
On 9/1/22 2:00 PM, Muchun Song wrote:
> The memory-notify-based approach aims to handle meory-less nodes, however, it just adds
> the complexity of code as pointed by David in thread [1]. The handling of memory-less
> nodes is introduced by commit 4faf8d950ec4 ("hugetlb: handle memory hot-plug events").
> From its commit message, we cannot find any necessity of handling this case. So, we can
> simply register/unregister sysfs entries in register_node/unregister_node to simlify the
> code.
Isn't that hotplug callback added because in hugetlb_register_all_nodes() we register
sysfs nodes only for N_MEMORY nodes?
>
> https://lore.kernel.org/linux-mm/60933ffc-b850-976c-78a0-0ee6e0ea9ef0@redhat.com/ [1]
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> drivers/base/node.c | 7 +++++--
> include/linux/node.h | 5 +++++
> mm/hugetlb.c | 37 ++++++++++---------------------------
> 3 files changed, 20 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index ed391cb09999..cf115d5a9b8a 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -608,10 +608,12 @@ static int register_node(struct node *node, int num)
> node->dev.groups = node_dev_groups;
> error = device_register(&node->dev);
>
> - if (error)
> + if (error) {
> put_device(&node->dev);
> - else
> + } else {
> + hugetlb_register_node(node);
> compaction_register_node(node);
> + }
>
I guess this will handle register of sysfs hugetlb files for new NUMA nodes
after hugetlb_initialized = true;
But what about N_CPU that can get memory added later. Do we need to update
hugetlb_register_all_nodes() to handle N_ONLINE?
> return error;
> }
> @@ -625,6 +627,7 @@ static int register_node(struct node *node, int num)
> */
> void unregister_node(struct node *node)
> {
> + hugetlb_unregister_node(node);
> compaction_unregister_node(node);
> node_remove_accesses(node);
> node_remove_caches(node);
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 427a5975cf40..f5d41498c2bf 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -138,6 +138,11 @@ 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
> +void hugetlb_register_node(struct node *node);
> +void hugetlb_unregister_node(struct node *node);
> +#endif
> #else
> static inline void node_dev_init(void)
> {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index d0617d64d718..722e862bb6be 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3898,6 +3898,7 @@ static void __init hugetlb_sysfs_init(void)
> }
>
> #ifdef CONFIG_NUMA
> +static bool hugetlb_initialized __ro_after_init;
>
> /*
> * node_hstate/s - associate per node hstate attributes, via their kobjects,
> @@ -3953,7 +3954,7 @@ static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
> * Unregister hstate attributes from a single node device.
> * No-op if no hstate attributes attached.
> */
> -static void hugetlb_unregister_node(struct node *node)
> +void hugetlb_unregister_node(struct node *node)
> {
> struct hstate *h;
> struct node_hstate *nhs = &node_hstates[node->dev.id];
> @@ -3983,19 +3984,22 @@ static void hugetlb_unregister_node(struct node *node)
> * Register hstate attributes for a single node device.
> * No-op if attributes already registered.
> */
> -static int hugetlb_register_node(struct node *node)
> +void hugetlb_register_node(struct node *node)
> {
> struct hstate *h;
> struct node_hstate *nhs = &node_hstates[node->dev.id];
> int err;
>
> + if (!hugetlb_initialized)
> + return;
> +
> if (nhs->hugepages_kobj)
> - return 0; /* already allocated */
> + return; /* already allocated */
>
> nhs->hugepages_kobj = kobject_create_and_add("hugepages",
> &node->dev.kobj);
> if (!nhs->hugepages_kobj)
> - return -ENOMEM;
> + return;
>
> for_each_hstate(h) {
> err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
> @@ -4005,28 +4009,9 @@ static int 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);
> - return -ENOMEM;
> + break;
> }
> }
> - 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);
> }
>
> /*
> @@ -4038,11 +4023,9 @@ static void __init hugetlb_register_all_nodes(void)
> {
> int nid;
>
> - get_online_mems();
> - hotplug_memory_notifier(hugetlb_memory_callback, 0);
> + hugetlb_initialized = true;
> for_each_node_state(nid, N_MEMORY)
Should this be for_each_online_node() ?
> hugetlb_register_node(node_devices[nid]);
> - put_online_mems();
> }
> #else /* !CONFIG_NUMA */
>
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