Re: [PATCH v2 05/34] mm: add utility functions for ptdesc

[Vishal Moola <vishal.moola@gmail.com>]

On Thu, May 25, 2023 at 1:26 PM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Thu, May 25, 2023 at 11:04:28AM -0700, Vishal Moola wrote:
> > On Thu, May 25, 2023 at 2:10 AM Mike Rapoport <rppt@kernel.org> wrote:
> > > > +
> > > > +static inline struct ptdesc *ptdesc_alloc(gfp_t gfp, unsigned int order)
> > > > +{
> > > > +     struct page *page = alloc_pages(gfp | __GFP_COMP, order);
> > > > +
> > > > +     return page_ptdesc(page);
> > > > +}
> > > > +
> > > > +static inline void ptdesc_free(struct ptdesc *pt)
> > > > +{
> > > > +     struct page *page = ptdesc_page(pt);
> > > > +
> > > > +     __free_pages(page, compound_order(page));
> > > > +}
> > >
> > > The ptdesc_{alloc,free} API does not sound right to me. The name
> > > ptdesc_alloc() implies the allocation of the ptdesc itself, rather than
> > > allocation of page table page. The same goes for free.
> >
> > I'm not sure I see the difference. Could you elaborate?
>
> I read ptdesc_alloc() as "allocate a ptdesc" rather than as "allocate a
> page for page table and return ptdesc pointing to that page". Seems very
> confusing to me already and it will be even more confusion when we'll start
> allocating actual ptdescs.

Hmm, I see what you're saying. I'm envisioning this function evolving into
one that allocates a ptdesc later. I don't see why we would need to have both a
page table page AND ptdesc at any point, but that may be a lack of knowledge
from my part.

I was thinking later, if necessary, we could make another function
(only to be used internally) to allocate page table pages.

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