Re: [PATCH 01/10] mm: page_ref_add_unless() does not trace 'u' argument

[Pasha Tatashin]

On Wed, Dec 8, 2021 at 3:55 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Wed, Dec 08, 2021 at 08:35:35PM +0000, Pasha Tatashin wrote:
> > In other page_ref_* functions all arguments and returns are traced, but
> > in page_ref_add_unless the 'u' argument which stands for unless boolean
> > is not traced. However, what is more confusing is that in the tracing
> > routine:
> >       __page_ref_mod_unless(struct page *page, int v, int u);
> >
> > The 'u' argument present, but instead a return value is passed into
> > this argument.
> >
> > Add a new template specific for page_ref_add_unless(), and trace all
> > arguments and the return value.
>
> The special casing of '1' for device pages is going away, so NAK
> to this user-visible change.

I can drop this patch, as it really intended to fix existing oddities
and missing info. However, I do not really understand your NAK reason.
Can you please explain about the special casing of "1" for device
pages?

Pasha