Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Sep 11, 2025 at 01:12:11PM -0700, Suren Baghdasaryan wrote:
> On Thu, Sep 11, 2025 at 1:01 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> >
> > On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> > > When freeing "tail" pages of a non-compount high-order page, we properly
> > > subtract the allocation tag counters, however later when these pages are
> > > released, alloc_tag_sub() will issue warnings because tags for these pages
> > > are NULL.
> > > This issue was originally anticipated by Vlastimil in his review [1] and
> > > then recently reported by David.
> > > Prevent warnings by marking the tags empty.
> > >
> > > [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> > >
> > > Suggested-by: David Wang <00107082@163.com>
> > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > > ---
> > >  mm/page_alloc.c | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 1760346bbd24..d21a411e807e 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
> > >               __free_frozen_pages(page, order, fpi_flags);
> > >       else if (!head) {
> > >               pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> > > -             while (order-- > 0)
> > > +             while (order-- > 0) {
> > > +                     /*
> > > +                      * The "tail" pages of this non-compound high-order
> > > +                      * page will have no code tags, so to avoid warnings
> > > +                      * mark them as empty.
> > > +                      */
> > > +                     clear_page_tag_ref(page + (1 << order));
> >
> > Do we need something similar for the release_pages() code path or is it
> > happening already?
> 
> Pages released with release_pages() should have valid tags, so I
> expect no warnings.
> 

Oh so this is orthogonal to your first patch which is replacing
__free_page with release_pages(). This non-compound high-order page is
not an issue in the codepath vm_module_tags_populate(), correct?