Re: [PATCH v1 1/4] mm: convert FPB_IGNORE_* into FPB_HONOR_*

[David Hildenbrand]

On 28.06.25 05:37, Dev Jain wrote:
> On 27/06/25 5:25 pm, David Hildenbrand wrote:
> > Honoring these PTE bits is the exception, so let's invert the meaning.
> >
> > With this change, most callers don't have to pass any flags.
> >
> > No functional change intended.
>
> FWIW I had proposed this kind of change earlier to Ryan (CCed) and
> he pointed out: "Doesn't that argument apply in reverse if you want
> to ignore something new in future?
>
> By default we are comparing all the bits in the pte when determining the batch.
> The flags request to ignore certain bits.

That statement is not true: as default we ignore the write and young 
bit. And we don't have flags for that ;)

Now we also ignore the dirty and soft-dity bit as default, unless told 
not to do that by one very specific caller.

> If we want to ignore extra bits in
> future, we add new flags and the existing callers don't need to be updated.

What stops you from using FPB_IGNORE_* for something else in the future?

As a side note, there are not that many relevant PTE bits to worry about 
in the near future ;)

I mean, uffd-wp, sure, ... and before we add a FPB_HONOR_UFFD_WP to all 
users to be safe (and changing the default to ignore), you could add a 
FPB_IGNORE_UFFD_WP first, to then check who really can tolerate just 
ignoring it (most of them, I assume).

--
Cheers,

David / dhildenb