Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add_memory()

David Hildenbrand
2019-12-10T10:10:02Z

On 10.12.19 11:04, Michal Hocko wrote:
> On Mon 09-12-19 12:43:40, Dan Williams wrote:
>> On Mon, Dec 9, 2019 at 12:24 PM Logan Gunthorpe <logang@deltatee.com> wrote:
>>>
>>>
>>>
>>> On 2019-12-09 12:23 p.m., David Hildenbrand wrote:
>>>> On 09.12.19 20:13, Logan Gunthorpe wrote:
> [...]
>>>>> #ifdef CONFIG_MEMORY_HOTPLUG
>>>>> -int arch_add_memory(int nid, u64 start, u64 size,
>>>>> +int arch_add_memory(int nid, u64 start, u64 size, pgprot_t prot,
>>>>> struct mhp_restrictions *restrictions)
>>>>
>>>> Can we fiddle that into "struct mhp_restrictions" instead?
>>>
>>> Yes, if that's what people want, it's pretty trivial to do. I chose not
>>> to do it that way because it doesn't get passed down to add_pages() and
>>> it's not really a "restriction". If I don't hear any objections, I will
>>> do that for v2.
>>
>> +1 to storing this information alongside the altmap in that structure.
>> However, I agree struct mhp_restrictions, with the MHP_MEMBLOCK_API
>> flag now gone, has lost all of its "restrictions". How about dropping
>> the 'flags' property and renaming the struct to 'struct
>> mhp_modifiers'?
>
> Hmm, this email somehow didn't end up in my inbox so I have missed it
> before replying.
>
> Well, mhp_modifiers makes some sense and it would reduce the API
> proliferation but how do you expect the prot part to be handled?
> I really do not want people to think about PAGE_KERNEL or which
> protection to use because my experience tells that this will get copied
> without much thinking or simply will break with some odd usecases.
> So how exactly this would be used?

I was thinking about exactly the same "issue".

1. default initialization via a function

memhp_modifier_default_init(&modified);

2. a flag that unlocks the prot field (default:0). Without the flag, it
is ignored. We can keep the current initialization then.

Other ideas?

--
Thanks,

David / dhildenb