[LSF/MM/BPF TOPIC] Reclaiming & documenting page flags

[Matthew Wilcox]

On Wed, Feb 07, 2024 at 05:51:44PM +0200, Mike Rapoport wrote:
> On Sun, Feb 04, 2024 at 09:34:01PM +0000, Matthew Wilcox wrote:
> > I'm doing my best to write documentation as I go.  I think we're a bit
> > better off than we were last year.  Do we have scripts to tell us which
> > public functions (ie EXPORT_SYMBOL and static inline functions in header
> > files) have kernel-doc?  And could we run them against kernels from, say,
> > April 2023, 2022, 2021, 2020, 2019 (and in two months against April 2024)
> > and see how we're doing in terms of percentage undocumented functions?
> 
> We didn't have such script, but it was easy to compare "grep
> EXPORT_SYMBOL\|static inline" with ".. c:function" in kernel-doc.
> We do improve slowly, but we are still below 50% with kernel-doc for
> EXPORT_SYMBOL functions and slightly above 10% for static inlines.

Thanks for doing this!  Data is good ;-)

I just came across an interesting example of a function which I believe
should NOT have kernel-doc.  But it should have documentation for why it
doesn't have kernel-doc!  Any thoughts about how we might accomplish that?

The example is filemap_range_has_writeback().  It's EXPORT_SYMBOL_GPL()
and it's a helper function for filemap_range_needs_writeback().
filemap_range_needs_writeback() has kernel-doc, but nobody should be
calling filemap_range_has_writeback() directly, so it shouldn't even
exist in the htmldocs.  But we should have a comment on it saying
"Use filemap_range_needs_writeback(), don't use this", in case anyone
discovers it.  And the existance of that comment should be enough to
tell our tools to not flag this as a function that needs kernel-doc.