On 9/16/21 4:30 PM, David Hildenbrand wrote:

On 16.09.21 07:32, Qi Zheng wrote:

quoted

On 9/15/21 10:59 PM, Jason Gunthorpe wrote:

quoted

On Wed, Sep 15, 2021 at 10:52:40PM +0800, Qi Zheng wrote:

quoted

I am going to split this patch series as follows:

1. Introduce the new dummy APIs, which is an empty implementation.
     But I will explain its semantics.
2. Merge #6, #7 and #8, and call these dummy APIs in any necessary
     location, and split some special cases into single patches, 
such as
     pagefault and gup, etc. So that we can explain in more detail the
     concurrency in these cases. For example, we don't need to hold any
     pte_refcount in the fast path in gup on the x86_64 platform. 
Because
     the PTE page can't be freed after the local CPU interrupt is 
closed
     in the fast path in gup.
3. Introduce CONFIG_FREE_USER_PTE and implement these empty dummy APIs.
4. Add a description document.

And I try to add a function that combines pte_offset_map() and
pte_try_get(). Maybe the func name is pte_try_map() recommended by
Jason, or keep the pte_offset_map() unchanged?

It is part of the transformation, add a
pte_try_map()/pte_undo_try_map() and replace all the pte_offset_map()
callsites that can use the new API with it. The idea was that try_map
would incorporate the pmd_trans_unstable/etc mess so searching for
trans_unstable is a good place to start finding candidates. Some are
simple, some are tricky.

Yes, I will search pte_offset_map()/pmd_trans_unstable/etc, and then
analyze the specific situation.

Maybe propose the new API first, before doing the actual implementation. 
Might safe you from doing some additional back-and-forth
work eventually.

OK, I prepare to propose all the dummy APIs in the step 1.

Thanks,
Qi