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

[Hugh Dickins]

On Mon, 21 Nov 2022, Kirill A. Shutemov wrote:
> On Fri, Nov 18, 2022 at 05:35:05PM -0800, Hugh Dickins wrote:
...
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1281,7 +1281,7 @@ void page_add_anon_rmap(struct page *page,
> >  	struct compound_mapcounts mapcounts;
> >  	int nr = 0, nr_pmdmapped = 0;
> >  	bool compound = flags & RMAP_COMPOUND;
> > -	bool first;
> > +	bool first = true;
> >  
> >  	if (unlikely(PageKsm(page)))
> >  		lock_page_memcg(page);
> 
> Other option is to drop PageTransHuge() check that you already claim to be
> redundant.
> 
> Or have else BUG() to catch cases where the helper called with
> compound=true on non-THP page.

I'm sticking with the "first = true".  I did receive a report of bloating
some tiny config a little, on the very first series, so I've been on guard
since then about adding THP code where the optimizer cannot see to remove
it: so do want to keep the PageTransHuge check in there.  Could be done
in other ways, yes, but I'd ended up feeling this was the best compromise.

Hugh