Re: [PATCH v4 1/6] libnvdimm/namespace: Make namespace size validation arch dependent

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

On 1/24/20 10:15 PM, Dan Williams wrote:
> On Thu, Jan 23, 2020 at 11:34 PM Aneesh Kumar K.V
> <aneesh.kumar@linux.ibm.com> wrote:
>>
>> On 1/24/20 11:27 AM, Dan Williams wrote:
>>> On Mon, Jan 20, 2020 at 6:08 AM Aneesh Kumar K.V
>>>
>>
>> ....
>>
>>>>
>>>> +unsigned long arch_namespace_map_size(void)
>>>> +{
>>>> +       return PAGE_SIZE;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(arch_namespace_map_size);
>>>> +
>>>> +
>>>>    static void __cpa_flush_all(void *arg)
>>>>    {
>>>>           unsigned long cache = (unsigned long)arg;
>>>> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
>>>> index 9df091bd30ba..a3476dbd2656 100644
>>>> --- a/include/linux/libnvdimm.h
>>>> +++ b/include/linux/libnvdimm.h
>>>> @@ -284,4 +284,5 @@ static inline void arch_invalidate_pmem(void *addr, size_t size)
>>>>    }
>>>>    #endif
>>>>
>>>> +unsigned long arch_namespace_map_size(void);
>>>
>>> This property is more generic than the nvdimm namespace mapping size,
>>> it's more the fundamental remap granularity that the architecture
>>> supports. So I would expect this to be defined in core header files.
>>> Something like:
>>>
>>> diff --git a/include/linux/io.h b/include/linux/io.h
>>> index a59834bc0a11..58b3b2091dbb 100644
>>> --- a/include/linux/io.h
>>> +++ b/include/linux/io.h
>>> @@ -155,6 +155,13 @@ enum {
>>>    void *memremap(resource_size_t offset, size_t size, unsigned long flags);
>>>    void memunmap(void *addr);
>>>
>>> +#ifndef memremap_min_align
>>> +static inline unsigned int memremap_min_align(void)
>>> +{
>>> +       return PAGE_SIZE;
>>> +}
>>> +#endif
>>> +
>>
>>
>> Should that be memremap_pages_min_align()?
> 
> No, and on second look it needs to be a common value that results in
> properly aligned / sized namespaces across architectures.
> 
> What would it take for Power to make it's minimum mapping granularity
> SUBSECTION_SIZE? The minute that the minimum alignment changes across
> architectures we lose compatibility.
> 
> The namespaces need to be sized such that the mode can be changed freely.
> 

Linux on ppc64 with hash translation use just one page size for direct 
mapping and that is 16MB.

-aneesh