Re: [PATCH v2 6/8] mm/memory_hotplug: Remove memory block devices before arch_remove_memory()

[Dan Williams]

On Tue, May 7, 2019 at 11:39 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> Let's factor out removing of memory block devices, which is only
> necessary for memory added via add_memory() and friends that created
> memory block devices. Remove the devices before calling
> arch_remove_memory().
>
> This finishes factoring out memory block device handling from
> arch_add_memory() and arch_remove_memory().

Also nice! makes it easier in the future for the "device-memory" use
case to not avoid messing up the typical memory hotplug flow.

>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: "mike.travis@xxxxxxx" <mike.travis@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andrew Banman <andrew.banman@xxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> Cc: Arun KS <arunks@xxxxxxxxxxxxxx>
> Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  drivers/base/memory.c  | 39 +++++++++++++++++++--------------------
>  drivers/base/node.c    | 11 ++++++-----
>  include/linux/memory.h |  2 +-
>  include/linux/node.h   |  6 ++----
>  mm/memory_hotplug.c    |  5 +++--
>  5 files changed, 31 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 862c202a18ca..47ff49058d1f 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -756,32 +756,31 @@ int hotplug_memory_register(unsigned long start, unsigned long size)
>         return ret;
>  }
>
> -static int remove_memory_section(struct mem_section *section)
> +/*
> + * Remove memory block devices for the given memory area. Start and size
> + * have to be aligned to memory block granularity. Memory block devices
> + * have to be offline.
> + */
> +void hotplug_memory_unregister(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);
>         struct memory_block *mem;
> +       unsigned long pfn;
>
> -       if (WARN_ON_ONCE(!present_section(section)))
> -               return;
> +       BUG_ON(!IS_ALIGNED(start, memory_block_size_bytes()));
> +       BUG_ON(!IS_ALIGNED(size, memory_block_size_bytes()));

Similar BUG_ON vs comments WARN_ON comments as the previous patch.

>
>         mutex_lock(&mem_sysfs_mutex);
> -
> -       /*
> -        * Some users of the memory hotplug do not want/need memblock to
> -        * track all sections. Skip over those.
> -        */
> -       mem = find_memory_block(section);
> -       if (!mem)
> -               goto out_unlock;
> -
> -       unregister_mem_sect_under_nodes(mem, __section_nr(section));
> -
> -       mem->section_count--;
> -       if (mem->section_count == 0)
> +       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_block_under_nodes(mem);
>                 unregister_memory(mem);
> -       else
> -               put_device(&mem->dev);
> -
> -out_unlock:
> +       }
>         mutex_unlock(&mem_sysfs_mutex);
>  }
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 8598fcbd2a17..04fdfa99b8bc 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -801,9 +801,10 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
>         return 0;
>  }
>
> -/* unregister memory section under all nodes that it spans */
> -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> -                                   unsigned long phys_index)
> +/*
> + * Unregister memory block device under all nodes that it spans.
> + */
> +int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>  {
>         NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
>         unsigned long pfn, sect_start_pfn, sect_end_pfn;
> @@ -816,8 +817,8 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
>                 return -ENOMEM;
>         nodes_clear(*unlinked_nodes);
>
> -       sect_start_pfn = section_nr_to_pfn(phys_index);
> -       sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
> +       sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
> +       sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
>         for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
>                 int nid;
>
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index 95505fbb5f85..aa236c2a0466 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -112,7 +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(unsigned long start, unsigned long size);
> -extern void unregister_memory_section(struct mem_section *);
> +void hotplug_memory_unregister(unsigned long start, unsigned long size);
>  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/node.h b/include/linux/node.h
> index 1a557c589ecb..02a29e71b175 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -139,8 +139,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
>  extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
>  extern int register_mem_sect_under_node(struct memory_block *mem_blk,
>                                                 void *arg);
> -extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> -                                          unsigned long phys_index);
> +extern int 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,
> @@ -176,8 +175,7 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk,
>  {
>         return 0;
>  }
> -static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> -                                                 unsigned long phys_index)
> +static inline int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>  {
>         return 0;
>  }
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 107f72952347..527fe4f9c620 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -519,8 +519,6 @@ static void __remove_section(struct zone *zone, struct mem_section *ms,
>         if (WARN_ON_ONCE(!valid_section(ms)))
>                 return;
>
> -       unregister_memory_section(ms);
> -
>         scn_nr = __section_nr(ms);
>         start_pfn = section_nr_to_pfn((unsigned long)scn_nr);
>         __remove_zone(zone, start_pfn);
> @@ -1844,6 +1842,9 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
>         memblock_free(start, size);
>         memblock_remove(start, size);
>
> +       /* remove memory block devices before removing memory */
> +       hotplug_memory_unregister(start, size);
> +
>         arch_remove_memory(nid, start, size, NULL);
>         __release_memory_resource(start, size);

Other than the BUG_ON concern you can add

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>