Re: [PATCH 4/9] mm, memory_hotplug: get rid of is_zone_device_section

[Jerome Glisse]

On Mon, Apr 10, 2017 at 01:03:46PM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> device memory hotplug hooks into regular memory hotplug only half way.
> It needs memory sections to track struct pages but there is no
> need/desire to associate those sections with memory blocks and export
> them to the userspace via sysfs because they cannot be onlined anyway.
> 
> This is currently expressed by for_device argument to arch_add_memory
> which then makes sure to associate the given memory range with
> ZONE_DEVICE. register_new_memory then relies on is_zone_device_section
> to distinguish special memory hotplug from the regular one. While this
> works now, later patches in this series want to move __add_zone outside
> of arch_add_memory path so we have to come up with something else.
> 
> Add want_memblock down the __add_pages path and use it to control
> whether the section->memblock association should be done. arch_add_memory
> then just trivially want memblock for everything but for_device hotplug.
> 
> remove_memory_section doesn't need is_zone_device_section either. We can
> simply skip all the memblock specific cleanup if there is no memblock
> for the given section.
> 
> This shouldn't introduce any functional change.
> 
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  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          | 22 ++++++++--------------
>  include/linux/memory_hotplug.h |  2 +-
>  mm/memory_hotplug.c            | 11 +++++++----
>  9 files changed, 22 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
> index 06cdaef54b2e..62085fd902e6 100644
> --- a/arch/ia64/mm/init.c
> +++ b/arch/ia64/mm/init.c
> @@ -657,7 +657,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  
>  	zone = pgdat->node_zones +
>  		zone_for_memory(nid, start, size, ZONE_NORMAL, for_device);
> -	ret = __add_pages(nid, zone, start_pfn, nr_pages);
> +	ret = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
>  
>  	if (ret)
>  		printk("%s: Problem encountered in __add_pages() as ret=%d\n",
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 5f844337de21..ea3e09a62f38 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -149,7 +149,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  	zone = pgdata->node_zones +
>  		zone_for_memory(nid, start, size, 0, for_device);
>  
> -	return __add_pages(nid, zone, start_pfn, nr_pages);
> +	return __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index bf5b8a0c4ff7..5c84346e5211 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -182,7 +182,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  			continue;
>  		nr_pages = (start_pfn + size_pages > zone_end_pfn) ?
>  			   zone_end_pfn - start_pfn : size_pages;
> -		rc = __add_pages(nid, zone, start_pfn, nr_pages);
> +		rc = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
>  		if (rc)
>  			break;
>  		start_pfn += nr_pages;
> diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
> index 75491862d900..a9d57f75ae8c 100644
> --- a/arch/sh/mm/init.c
> +++ b/arch/sh/mm/init.c
> @@ -498,7 +498,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  	ret = __add_pages(nid, pgdat->node_zones +
>  			zone_for_memory(nid, start, size, ZONE_NORMAL,
>  			for_device),
> -			start_pfn, nr_pages);
> +			start_pfn, nr_pages, !for_device);
>  	if (unlikely(ret))
>  		printk("%s: Failed, __add_pages() == %d\n", __func__, ret);
>  
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index c68078fd06fd..4b0f05328af0 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -834,7 +834,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  	unsigned long start_pfn = start >> PAGE_SHIFT;
>  	unsigned long nr_pages = size >> PAGE_SHIFT;
>  
> -	return __add_pages(nid, zone, start_pfn, nr_pages);
> +	return __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7eef17239378..39cfaee93975 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -652,7 +652,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  
>  	init_memory_mapping(start, start + size);
>  
> -	ret = __add_pages(nid, zone, start_pfn, nr_pages);
> +	ret = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
>  	WARN_ON_ONCE(ret);
>  
>  	/* update max_pfn, max_low_pfn and high_memory */
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index cc4f1d0cbffe..89c15e942852 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -685,14 +685,6 @@ static int add_memory_block(int base_section_nr)
>  	return 0;
>  }
>  
> -static bool is_zone_device_section(struct mem_section *ms)
> -{
> -	struct page *page;
> -
> -	page = sparse_decode_mem_map(ms->section_mem_map, __section_nr(ms));
> -	return is_zone_device_page(page);
> -}
> -
>  /*
>   * need an interface for the VM to add new memory regions,
>   * but without onlining it.
> @@ -702,9 +694,6 @@ int register_new_memory(int nid, struct mem_section *section)
>  	int ret = 0;
>  	struct memory_block *mem;
>  
> -	if (is_zone_device_section(section))
> -		return 0;
> -
>  	mutex_lock(&mem_sysfs_mutex);
>  
>  	mem = find_memory_block(section);
> @@ -741,11 +730,16 @@ static int remove_memory_section(unsigned long node_id,
>  {
>  	struct memory_block *mem;
>  
> -	if (is_zone_device_section(section))
> -		return 0;
> -
>  	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)
> +		return 0;
> +

Another bug above spoted by Evgeny Baskakov from NVidia, mutex unlock
is missing ie something like:

if (!mem) {
	mutex_unlock(&mem_sysfs_mutex);
	return 0;
}

Between when are you planning on reposting ? I was hoping sometime soon
so i can repost HMM on top. I know with springtime celebration eveyrone
is out collecting chocolate eggs :)

Cheers,
Jérôme