Re: [PATCH v2 0/9] Free user PTE page table pages

[Qi Zheng]

On 9/15/21 10:59 PM, Jason Gunthorpe wrote:
> On Wed, Sep 15, 2021 at 10:52:40PM +0800, Qi Zheng wrote:
> > 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.

> When you get to step 3 you just change pte_try_map() and the callsites
> don't need changing.
>
> Jason

Thanks,
Qi