Re: [PATCH 1/3] mm,thp,rmap: subpages_mapcount of PTE-mapped subpages

[Hugh Dickins <hughd@google.com>]

On Mon, 21 Nov 2022, Kirill A. Shutemov wrote:
> On Fri, Nov 18, 2022 at 01:12:03AM -0800, Hugh Dickins wrote:
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Thanks a lot for all these, Kirill.

> 
> Few minor nitpicks below.
> 
...
> >  static inline void page_dup_file_rmap(struct page *page, bool compound)
> >  {
> > -	if (PageCompound(page))
> > -		page_dup_compound_rmap(page, compound);
> > -	else
> > +	if (likely(!compound /* page is mapped by PTE */))
> 
> I'm not a fan of this kind of comments.
> 
> Maybe move above the line (here and below)?

Okay, done throughout.  I wouldn't have added those comments, but Linus
had another "simmering hatred", of the "compound" arguments: he found
them very confusing.

The real fix is to rename them, probably to pmd_mapped; or better, pass
down an int nr_pages as he suggested; but I'm wary of the HPAGE_NR_PAGES
build bug, and it wants to be propagated through various other files
(headers and mlock.c, maybe more) - not a cleanup to get into now.

> 
> >  		atomic_inc(&page->_mapcount);
> > +	else
> > +		page_dup_compound_rmap(page);
> >  }
...
> > @@ -1176,20 +1157,16 @@ void page_dup_compound_rmap(struct page *page, bool compound)
> >  	 * Note that hugetlb does not call page_add_file_rmap():
> >  	 * here is where hugetlb shared page mapcount is raised.
> >  	 */
> > -	if (PageHuge(page)) {
> > -		atomic_inc(compound_mapcount_ptr(page));
> > -		return;
> > -	}
> > +	if (PageHuge(head)) {
> > +		atomic_inc(compound_mapcount_ptr(head));
> >  
> 
> Remove the newline?

It was intentional there, I thought it was easier to read that way;
but since this gets reverted in the next patch, I've no reason to
fight over it - removed.

Hugh