Re: [PATCH v5 19/25] arm64/mm: Wire up PTE_CONT for user mappings

David Hildenbrand
2024-02-12T13:54:33Z

>> If so, I wonder if we could instead do that comparison modulo the access/dirty
>> bits,
>
> I think that would work - but will need to think a bit more on it.
>
>> and leave ptep_get_lockless() only reading a single entry?
>
> I think we will need to do something a bit less fragile. ptep_get() does collect
> the access/dirty bits so its confusing if ptep_get_lockless() doesn't IMHO. So
> we will likely want to rename the function and make its documentation explicit
> that it does not return those bits.
>
> ptep_get_lockless_noyoungdirty()? yuk... Any ideas?
>
> Of course if I could convince you the current implementation is safe, I might be
> able to sidestep this optimization until a later date?

As discussed (and pointed out abive), there might be quite some
callsites where we don't really care about uptodate accessed/dirty bits
-- where ptep_get() is used nowadays.

One way to approach that I had in mind was having an explicit interface:

ptep_get()
ptep_get_uptodate()
ptep_get_lockless()
ptep_get_lockless_uptodate()

Especially the last one might not be needed.

Futher, "uptodate" might not be the best choice because of
PageUptodate() and friends. But it's better than
"youngdirty"/"noyoungdirty" IMHO.

Of course, any such changes require care and are better done one step at
at time separately.

--
Cheers,

David / dhildenb