[PATCH v6 2/7] dax: support dirty DAX entries in radix tree

[Dan Williams]

On Wed, Dec 30, 2015 at 12:02 AM, Bob Liu <bob.liu at oracle.com> wrote:
> Hi Ross,
>
> On 12/24/2015 03:39 AM, Ross Zwisler wrote:
>> Add support for tracking dirty DAX entries in the struct address_space
>> radix tree.  This tree is already used for dirty page writeback, and it
>> already supports the use of exceptional (non struct page*) entries.
>>
>> In order to properly track dirty DAX pages we will insert new exceptional
>> entries into the radix tree that represent dirty DAX PTE or PMD pages.
>
> I may get it wrong, but there is "struct page" for persistent memory after
> "[PATCH v4 00/18]get_user_pages() for dax pte and pmd mappings".
> So why not just add "struct page" to radix tree directly just like normal page cache?
>
> Then we don't need to deal with any exceptional entries and special writeback.

That "struct page" is optional and fsync/msync needs to operate in its absence.