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

[David Hildenbrand]

On 16.09.21 07:32, Qi Zheng wrote:
> 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.

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


--
Thanks,

David / dhildenb