linux-kernel - Re: [PATCH v1 1/4] mm/memory_hotplug: Release memory resource after arch_remove

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Date:   Wed, 10 Apr 2019 10:07:24 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Wei Yang <richard.weiyang@...il.com>, Qian Cai <cai@....pw>,
        Arun KS <arunks@...eaurora.org>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH v1 1/4] mm/memory_hotplug: Release memory resource after
 arch_remove_memory()

On 10.04.19 00:41, Andrew Morton wrote:
> On Tue,  9 Apr 2019 12:01:45 +0200 David Hildenbrand <david@...hat.com> wrote:
> 
>> __add_pages() doesn't add the memory resource, so __remove_pages()
>> shouldn't remove it. Let's factor it out. Especially as it is a special
>> case for memory used as system memory, added via add_memory() and
>> friends.
>>
>> We now remove the resource after removing the sections instead of doing
>> it the other way around. I don't think this change is problematic.
>>
>> add_memory()
>> 	register memory resource
>> 	arch_add_memory()
>>
>> remove_memory
>> 	arch_remove_memory()
>> 	release memory resource
>>
>> While at it, explain why we ignore errors and that it only happeny if
>> we remove memory in a different granularity as we added it.
> 
> Seems sane.
> 
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1820,6 +1806,25 @@ void try_offline_node(int nid)
>>  }
>>  EXPORT_SYMBOL(try_offline_node);
>>  
>> +static void __release_memory_resource(u64 start, u64 size)
>> +{
>> +	int ret;
>> +
>> +	/*
>> +	 * When removing memory in the same granularity as it was added,
>> +	 * this function never fails. It might only fail if resources
>> +	 * have to be adjusted or split. We'll ignore the error, as
>> +	 * removing of memory cannot fail.
>> +	 */
>> +	ret = release_mem_region_adjustable(&iomem_resource, start, size);
>> +	if (ret) {
>> +		resource_size_t endres = start + size - 1;
>> +
>> +		pr_warn("Unable to release resource <%pa-%pa> (%d)\n",
>> +			&start, &endres, ret);
>> +	}
>> +}
> 
> The types seem confused here.  Should `start' and `size' be
> resource_size_t?  Or maybe phys_addr_t.

Hmm, right now it has the same prototype as register_memory_resource. I
guess using resource_size_t is the right thing to do.

> 
> release_mem_region_adjustable() takes resource_size_t's.
> 
> Is %pa the way to print a resource_size_t?  I guess it happens to work
> because resource_size_t happens to map onto phys_addr_t, which isn't
> ideal.

Documentation/core-api/printk-formats.rst

"
	%pa[p]	0x01234567 or 0x0123456789abcdef

For printing a phys_addr_t type (and its derivatives, such as
resource_size_t) ...
"


Care to fixup both u64 to resource_size_t? Or should I send a patch?
Whatever you prefer.

Thanks!

-- 

Thanks,

David / dhildenb