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SubjectRe: [PATCH RFC 2/3] mm/memory_hotplug: Create memory block devices after arch_add_memory()
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On 08.04.19 12:12, David Hildenbrand wrote:
> Only memory added via add_memory() and friends will need memory
> block devices - only memory to be used via the buddy and to be onlined/
> offlined by user space in memory block granularity.
>
> Move creation of memory block devices out of arch_add_memory(). 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.
>
> Issue 1: __add_pages() does not remove pages in case something went
> wrong. If this is the case, we would now no longer create memory block
> devices for such "partially added memory". So the memory would not be
> usable/onlinable. Bad? Or related to issue 2 (e.g. fix __add_pages()
> to remove any parts that were added in case of an error). Functions that
> fail and don't clean up are not that nice.
>
> Issue 2: In case we can't add memory block devices, and we don't have
> HOTREMOVE, we can't remove the pages via arch_remove_pages. Maybe we should
> try to get rid of CONFIG_MEMORY_HOTREMOVE, so we can handle all failures
> in a nice way? Or at least allow arch_remove_pages() and friends, so a
> subset of CONFIG_MEMORY_HOTREMOVE.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/base/memory.c | 67 +++++++++++++++++++++++++-----------------
> include/linux/memory.h | 2 +-
> mm/memory_hotplug.c | 17 +++++++----
> 3 files changed, 53 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index d9ebb89816f7..847b33061e2e 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -701,44 +701,57 @@ static int add_memory_block(int base_section_nr)
> return 0;
> }
>
> -/*
> - * need an interface for the VM to add new memory regions,
> - * but without onlining it.
> - */
> -int hotplug_memory_register(int nid, struct mem_section *section)
> +static void unregister_memory(struct memory_block *memory)
> {
> - int ret = 0;
> + BUG_ON(memory->dev.bus != &memory_subsys);
> +
> + /* drop the ref. we got via find_memory_block() */
> + put_device(&memory->dev);
> + device_unregister(&memory->dev);
> +}
> +
> +int hotplug_memory_register(unsigned long start, unsigned long size)
> +{
> + 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()));
>
> - 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);
> + 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;
> }
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> -static void
> -unregister_memory(struct memory_block *memory)
> -{
> - BUG_ON(memory->dev.bus != &memory_subsys);
> -
> - /* drop the ref. we got in remove_memory_section() */
> - put_device(&memory->dev);
> - device_unregister(&memory->dev);
> -}
> -
> 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 a6ddefc60517..e275dc775834 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);
> #ifdef CONFIG_MEMORY_HOTREMOVE
> extern int unregister_memory_section(struct mem_section *);
> #endif
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 680dcc67f9d5..13ee0a26e034 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -260,11 +260,7 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
> 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 0;
> }
>
> /*
> @@ -1125,6 +1121,17 @@ 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);
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> + if (ret) {
> + arch_remove_memory(nid, start, size, NULL);
> + goto error;
> + }
> +#else
> + WARN_ON(ret);
> +#endif
> +
> 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.
>

FWIW, I think we should first try to make sure arch_remove_memory()
cannot fail / will not ignore errors if possible. There are still some
things in there that need more re-factoring first.

--

Thanks,

David / dhildenb

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