Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices after arch_add_memory()

Dan Williams
2019-05-07T21:17:16Z

On Tue, May 7, 2019 at 11:38 AM David Hildenbrand <david@redhat.com> wrote:
>
> Only memory to be added to the buddy and to be onlined/offlined by
> user space using memory block devices needs (and should have!) memory
> block devices.
>
> Factor out creation of memory block devices Create all devices after
> arch_add_memory() succeeded. We can later drop the want_memblock parameter,
> because it is now effectively stale.
>
> Only after memory block devices have been added, memory can be onlined
> by user space. This implies, that memory is not visible to user space at
> all before arch_add_memory() succeeded.

Nice!

>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: "mike.travis@hpe.com" <mike.travis@hpe.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Andrew Banman <andrew.banman@hpe.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Cc: Arun KS <arunks@codeaurora.org>
> Cc: Mathieu Malaterre <malat@debian.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/base/memory.c | 70 ++++++++++++++++++++++++++----------------
> include/linux/memory.h | 2 +-
> mm/memory_hotplug.c | 15 ++++-----
> 3 files changed, 53 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 6e0cb4fda179..862c202a18ca 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -701,44 +701,62 @@ static int add_memory_block(int base_section_nr)
> return 0;
> }
>
> +static void unregister_memory(struct memory_block *memory)
> +{
> + BUG_ON(memory->dev.bus != &memory_subsys);

Given this should never happen and only a future kernel developer
might trip over it, do we really need to kill that developer's
machine? I.e. s/BUG/WARN/? I guess an argument can be made to move
such a change that to a follow-on patch since you're just preserving
existing behavior, but I figure might as well address these as the
code is refactored.

> +
> + /* drop the ref. we got via find_memory_block() */
> + put_device(&memory->dev);
> + device_unregister(&memory->dev);
> +}
> +
> /*
> - * need an interface for the VM to add new memory regions,
> - * but without onlining it.
> + * Create memory block devices for the given memory area. Start and size
> + * have to be aligned to memory block granularity. Memory block devices
> + * will be initialized as offline.
> */
> -int hotplug_memory_register(int nid, struct mem_section *section)
> +int hotplug_memory_register(unsigned long start, unsigned long size)
> {
> - int ret = 0;
> + unsigned long block_nr_pages = memory_block_size_bytes() >> PAGE_SHIFT;
> + unsigned long start_pfn = PFN_DOWN(start);
> + unsigned long end_pfn = start_pfn + (size >> PAGE_SHIFT);
> + unsigned long pfn;
> struct memory_block *mem;
> + int ret = 0;
>
> - mutex_lock(&mem_sysfs_mutex);
> + BUG_ON(!IS_ALIGNED(start, memory_block_size_bytes()));
> + BUG_ON(!IS_ALIGNED(size, memory_block_size_bytes()));

Perhaps:

if (WARN_ON(...))
return -EINVAL;

>
> - mem = find_memory_block(section);
> - if (mem) {
> - mem->section_count++;
> - put_device(&mem->dev);
> - } else {
> - ret = init_memory_block(&mem, section, MEM_OFFLINE);
> + mutex_lock(&mem_sysfs_mutex);
> + for (pfn = start_pfn; pfn != end_pfn; pfn += block_nr_pages) {
> + mem = find_memory_block(__pfn_to_section(pfn));
> + if (mem) {
> + WARN_ON_ONCE(false);

?? Isn't that a nop?

> + put_device(&mem->dev);
> + continue;
> + }
> + ret = init_memory_block(&mem, __pfn_to_section(pfn),
> + MEM_OFFLINE);
> if (ret)
> - goto out;
> - mem->section_count++;
> + break;
> + mem->section_count = memory_block_size_bytes() /
> + MIN_MEMORY_BLOCK_SIZE;
> + }
> + if (ret) {
> + end_pfn = pfn;
> + for (pfn = start_pfn; pfn != end_pfn; pfn += block_nr_pages) {
> + mem = find_memory_block(__pfn_to_section(pfn));
> + if (!mem)
> + continue;
> + mem->section_count = 0;
> + unregister_memory(mem);
> + }
> }
> -
> -out:
> mutex_unlock(&mem_sysfs_mutex);
> return ret;
> }
>
> -static void
> -unregister_memory(struct memory_block *memory)
> -{
> - BUG_ON(memory->dev.bus != &memory_subsys);
> -
> - /* drop the ref. we got via find_memory_block() */
> - put_device(&memory->dev);
> - device_unregister(&memory->dev);
> -}
> -
> -void unregister_memory_section(struct mem_section *section)
> +static int remove_memory_section(struct mem_section *section)
> {
> struct memory_block *mem;
>
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index 474c7c60c8f2..95505fbb5f85 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -111,7 +111,7 @@ extern int register_memory_notifier(struct notifier_block *nb);
> extern void unregister_memory_notifier(struct notifier_block *nb);
> extern int register_memory_isolate_notifier(struct notifier_block *nb);
> extern void unregister_memory_isolate_notifier(struct notifier_block *nb);
> -int hotplug_memory_register(int nid, struct mem_section *section);
> +int hotplug_memory_register(unsigned long start, unsigned long size);
> extern void unregister_memory_section(struct mem_section *);
> extern int memory_dev_init(void);
> extern int memory_notify(unsigned long val, void *v);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 7b5439839d67..e1637c8a0723 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -258,13 +258,7 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
> return -EEXIST;
>
> ret = sparse_add_one_section(nid, phys_start_pfn, altmap);
> - if (ret < 0)
> - return ret;
> -
> - if (!want_memblock)
> - return 0;
> -
> - return hotplug_memory_register(nid, __pfn_to_section(phys_start_pfn));
> + return ret < 0 ? ret : 0;
> }
>
> /*
> @@ -1106,6 +1100,13 @@ int __ref add_memory_resource(int nid, struct resource *res)
> if (ret < 0)
> goto error;
>
> + /* create memory block devices after memory was added */
> + ret = hotplug_memory_register(start, size);
> + if (ret) {
> + arch_remove_memory(nid, start, size, NULL);
> + goto error;
> + }
> +
> if (new_node) {
> /* If sysfs file of new node can't be created, cpu on the node
> * can't be hot-added. There is no rollback way now.
> --
> 2.20.1
>