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Subject: Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices
 after arch_add_memory()
To:     linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
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        Dan Williams <dan.j.williams@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        "mike.travis@hpe.com" <mike.travis@hpe.com>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Banman <andrew.banman@hpe.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Qian Cai <cai@lca.pw>, Wei Yang <richard.weiyang@gmail.com>,
        Arun KS <arunks@codeaurora.org>,
        Mathieu Malaterre <malat@debian.org>
References: <20190507183804.5512-1-david@redhat.com>
 <20190507183804.5512-5-david@redhat.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <094f6f72-b02f-585f-6ffa-d631c71808d6@redhat.com>
Date:   Wed, 8 May 2019 10:35:26 +0200
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On 07.05.19 20:38, David Hildenbrand 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.
> 
> 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);
> +
> +	/* 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()));
>  
> -	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;
>  }
>  
> -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)
>  {

The function change is misplaces in this patch will drop it so this
patch compiles without the other patches.


-- 

Thanks,

David / dhildenb