Subject: Re: [PATCH v3 06/11] mm/memory_hotplug: Allow arch_remove_pages() without CONFIG_MEMORY_HOTREMOVE

From: Michal Hocko <[email-masked]>
Date: Mon, 1 Jul 2019 10:01:41 +0200

On Mon 27-05-19 13:11:47, David Hildenbrand wrote:
> We want to improve error handling while adding memory by allowing
> to use arch_remove_memory() and __remove_pages() even if
> CONFIG_MEMORY_HOTREMOVE is not set to e.g., implement something like:
> 
> 	arch_add_memory()
> 	rc = do_something();
> 	if (rc) {
> 		arch_remove_memory();
> 	}
> 
> We won't get rid of CONFIG_MEMORY_HOTREMOVE for now, as it will require
> quite some dependencies for memory offlining.

If we cannot really remove CONFIG_MEMORY_HOTREMOVE altogether then why
not simply add an empty placeholder for arch_remove_memory when the
config is disabled?
 
> Cc: Tony Luck <[email-masked]>
> Cc: Fenghua Yu <[email-masked]>
> Cc: Benjamin Herrenschmidt <[email-masked]>
> Cc: Paul Mackerras <[email-masked]>
> Cc: Michael Ellerman <[email-masked]>
> Cc: Martin Schwidefsky <[email-masked]>
> Cc: Heiko Carstens <[email-masked]>
> Cc: Yoshinori Sato <[email-masked]>
> Cc: Rich Felker <[email-masked]>
> Cc: Dave Hansen <[email-masked]>
> Cc: Andy Lutomirski <[email-masked]>
> Cc: Peter Zijlstra <[email-masked]>
> Cc: Thomas Gleixner <[email-masked]>
> Cc: Ingo Molnar <[email-masked]>
> Cc: Borislav Petkov <[email-masked]>
> Cc: "H. Peter Anvin" <[email-masked]>
> Cc: Greg Kroah-Hartman <[email-masked]>
> Cc: "Rafael J. Wysocki" <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Michal Hocko <[email-masked]>
> Cc: Mike Rapoport <[email-masked]>
> Cc: David Hildenbrand <[email-masked]>
> Cc: Oscar Salvador <[email-masked]>
> Cc: "Kirill A. Shutemov" <[email-masked]>
> Cc: Alex Deucher <[email-masked]>
> Cc: "David S. Miller" <[email-masked]>
> Cc: Mark Brown <[email-masked]>
> Cc: Chris Wilson <[email-masked]>
> Cc: Christophe Leroy <[email-masked]>
> Cc: Nicholas Piggin <[email-masked]>
> Cc: Vasily Gorbik <[email-masked]>
> Cc: Rob Herring <[email-masked]>
> Cc: Masahiro Yamada <[email-masked]>
> Cc: "[email-masked]" <[email-masked]>
> Cc: Andrew Banman <[email-masked]>
> Cc: Pavel Tatashin <[email-masked]>
> Cc: Wei Yang <[email-masked]>
> Cc: Arun KS <[email-masked]>
> Cc: Qian Cai <[email-masked]>
> Cc: Mathieu Malaterre <[email-masked]>
> Cc: Baoquan He <[email-masked]>
> Cc: Logan Gunthorpe <[email-masked]>
> Cc: Anshuman Khandual <[email-masked]>
> Signed-off-by: David Hildenbrand <[email-masked]>
> ---
>  arch/arm64/mm/mmu.c            | 2 --
>  arch/ia64/mm/init.c            | 2 --
>  arch/powerpc/mm/mem.c          | 2 --
>  arch/s390/mm/init.c            | 2 --
>  arch/sh/mm/init.c              | 2 --
>  arch/x86/mm/init_32.c          | 2 --
>  arch/x86/mm/init_64.c          | 2 --
>  drivers/base/memory.c          | 2 --
>  include/linux/memory.h         | 2 --
>  include/linux/memory_hotplug.h | 2 --
>  mm/memory_hotplug.c            | 2 --
>  mm/sparse.c                    | 6 ------
>  12 files changed, 28 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index e569a543c384..9ccd7539f2d4 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1084,7 +1084,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
>  			   restrictions);
>  }
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void arch_remove_memory(int nid, u64 start, u64 size,
>  			struct vmem_altmap *altmap)
>  {
> @@ -1103,4 +1102,3 @@ void arch_remove_memory(int nid, u64 start, u64 size,
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  }
>  #endif
> -#endif
> diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
> index d28e29103bdb..aae75fd7b810 100644
> --- a/arch/ia64/mm/init.c
> +++ b/arch/ia64/mm/init.c
> @@ -681,7 +681,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	return ret;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void arch_remove_memory(int nid, u64 start, u64 size,
>  			struct vmem_altmap *altmap)
>  {
> @@ -693,4 +692,3 @@ void arch_remove_memory(int nid, u64 start, u64 size,
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  }
>  #endif
> -#endif
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index e885fe2aafcc..e4bc2dc3f593 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -130,7 +130,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
>  	return __add_pages(nid, start_pfn, nr_pages, restrictions);
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void __ref arch_remove_memory(int nid, u64 start, u64 size,
>  			     struct vmem_altmap *altmap)
>  {
> @@ -164,7 +163,6 @@ void __ref arch_remove_memory(int nid, u64 start, u64 size,
>  		pr_warn("Hash collision while resizing HPT\n");
>  }
>  #endif
> -#endif /* CONFIG_MEMORY_HOTPLUG */
>  
>  #ifndef CONFIG_NEED_MULTIPLE_NODES
>  void __init mem_topology_setup(void)
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 14955e0a9fcf..ffb81fe95c77 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -239,7 +239,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	return rc;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void arch_remove_memory(int nid, u64 start, u64 size,
>  			struct vmem_altmap *altmap)
>  {
> @@ -251,5 +250,4 @@ void arch_remove_memory(int nid, u64 start, u64 size,
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  	vmem_remove_mapping(start, size);
>  }
> -#endif
>  #endif /* CONFIG_MEMORY_HOTPLUG */
> diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
> index 13c6a6bb5fd9..dfdbaa50946e 100644
> --- a/arch/sh/mm/init.c
> +++ b/arch/sh/mm/init.c
> @@ -429,7 +429,6 @@ int memory_add_physaddr_to_nid(u64 addr)
>  EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
>  #endif
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void arch_remove_memory(int nid, u64 start, u64 size,
>  			struct vmem_altmap *altmap)
>  {
> @@ -440,5 +439,4 @@ void arch_remove_memory(int nid, u64 start, u64 size,
>  	zone = page_zone(pfn_to_page(start_pfn));
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  }
> -#endif
>  #endif /* CONFIG_MEMORY_HOTPLUG */
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index f265a4316179..4068abb9427f 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -860,7 +860,6 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	return __add_pages(nid, start_pfn, nr_pages, restrictions);
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  void arch_remove_memory(int nid, u64 start, u64 size,
>  			struct vmem_altmap *altmap)
>  {
> @@ -872,7 +871,6 @@ void arch_remove_memory(int nid, u64 start, u64 size,
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  }
>  #endif
> -#endif
>  
>  int kernel_set_to_readonly __read_mostly;
>  
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 693aaf28d5fe..8335ac6e1112 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1196,7 +1196,6 @@ void __ref vmemmap_free(unsigned long start, unsigned long end,
>  	remove_pagetable(start, end, false, altmap);
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  static void __meminit
>  kernel_physical_mapping_remove(unsigned long start, unsigned long end)
>  {
> @@ -1221,7 +1220,6 @@ void __ref arch_remove_memory(int nid, u64 start, u64 size,
>  	__remove_pages(zone, start_pfn, nr_pages, altmap);
>  	kernel_physical_mapping_remove(start, start + size);
>  }
> -#endif
>  #endif /* CONFIG_MEMORY_HOTPLUG */
>  
>  static struct kcore_list kcore_vsyscall;
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index f914fa6fe350..ac17c95a5f28 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -727,7 +727,6 @@ int hotplug_memory_register(int nid, struct mem_section *section)
>  	return ret;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  static void
>  unregister_memory(struct memory_block *memory)
>  {
> @@ -766,7 +765,6 @@ void unregister_memory_section(struct mem_section *section)
>  out_unlock:
>  	mutex_unlock(&mem_sysfs_mutex);
>  }
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  
>  /* return true if the memory block is offlined, otherwise, return false */
>  bool is_memblock_offlined(struct memory_block *mem)
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index e1dc1bb2b787..474c7c60c8f2 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -112,9 +112,7 @@ 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);
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  extern void unregister_memory_section(struct mem_section *);
> -#endif
>  extern int memory_dev_init(void);
>  extern int memory_notify(unsigned long val, void *v);
>  extern int memory_isolate_notify(unsigned long val, void *v);
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index ae892eef8b82..2d4de313926d 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -123,12 +123,10 @@ static inline bool movable_node_is_enabled(void)
>  	return movable_node_enabled;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  extern void arch_remove_memory(int nid, u64 start, u64 size,
>  			       struct vmem_altmap *altmap);
>  extern void __remove_pages(struct zone *zone, unsigned long start_pfn,
>  			   unsigned long nr_pages, struct vmem_altmap *altmap);
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  
>  /*
>   * Do we want sysfs memblock files created. This will allow userspace to online
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 762887b2358b..4b9d2974f86c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -318,7 +318,6 @@ int __ref __add_pages(int nid, unsigned long phys_start_pfn,
>  	return err;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  /* find the smallest valid pfn in the range [start_pfn, end_pfn) */
>  static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
>  				     unsigned long start_pfn,
> @@ -582,7 +581,6 @@ void __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
>  
>  	set_zone_contiguous(zone);
>  }
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  
>  int set_online_page_callback(online_page_callback_t callback)
>  {
> diff --git a/mm/sparse.c b/mm/sparse.c
> index fd13166949b5..d1d5e05f5b8d 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -604,7 +604,6 @@ static void __kfree_section_memmap(struct page *memmap,
>  
>  	vmemmap_free(start, end, altmap);
>  }
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  static void free_map_bootmem(struct page *memmap)
>  {
>  	unsigned long start = (unsigned long)memmap;
> @@ -612,7 +611,6 @@ static void free_map_bootmem(struct page *memmap)
>  
>  	vmemmap_free(start, end, NULL);
>  }
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  #else
>  static struct page *__kmalloc_section_memmap(void)
>  {
> @@ -651,7 +649,6 @@ static void __kfree_section_memmap(struct page *memmap,
>  			   get_order(sizeof(struct page) * PAGES_PER_SECTION));
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  static void free_map_bootmem(struct page *memmap)
>  {
>  	unsigned long maps_section_nr, removing_section_nr, i;
> @@ -681,7 +678,6 @@ static void free_map_bootmem(struct page *memmap)
>  			put_page_bootmem(page);
>  	}
>  }
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>  
>  /**
> @@ -746,7 +742,6 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
>  	return ret;
>  }
>  
> -#ifdef CONFIG_MEMORY_HOTREMOVE
>  #ifdef CONFIG_MEMORY_FAILURE
>  static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
>  {
> @@ -823,5 +818,4 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
>  			PAGES_PER_SECTION - map_offset);
>  	free_section_usemap(memmap, usemap, altmap);
>  }
> -#endif /* CONFIG_MEMORY_HOTREMOVE */
>  #endif /* CONFIG_MEMORY_HOTPLUG */
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs