On Mon, Dec 9, 2024 at 3:22 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 09.12.24 13:33, Mateusz Guzik wrote: > > That is to say I think this thread just about exhausted the time > > warranted by this patch. No hard feelz if it gets dropped, but then I > > do strongly suggest adding a justification to the extra load. > > Maybe it's sufficient for now to simply do your change with a comment: > > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h > index 8c236c651d1d6..1efc992ad5687 100644 > --- a/include/linux/page_ref.h > +++ b/include/linux/page_ref.h > @@ -234,7 +234,13 @@ static inline bool page_ref_add_unless(struct page *page, int nr, int u) > > rcu_read_lock(); > /* avoid writing to the vmemmap area being remapped */ > - if (!page_is_fake_head(page) && page_ref_count(page) != u) > + if (!page_is_fake_head(page)) > + /* > + * atomic_add_unless() will currently never modify the value > + * if it already is u. If that ever changes, we'd have to have > + * a separate check here, such that we won't be writing to > + * write-protected vmemmap areas. > + */ > ret = atomic_add_unless(&page->_refcount, nr, u); > rcu_read_unlock(); > > > It would bail out during testing ... hopefully, such that we can detect any such change. > Not my call to make, but looks good. ;) fwiw I don't need any credit and I would be more than happy if you just submitted the thing as your own without me being mentioned. *No* cc would also be appreciated. -- Mateusz Guzik <mjguzik gmail.com>
