Re: [PATCH] [RFC] mm: add kmem_cache_create_rcu()

[Jann Horn <jannh@google.com>]

On Tue, Aug 27, 2024 at 4:05 PM Vlastimil Babka <vbabka@suse.cz> wrote:
> On 8/26/24 18:04, Christian Brauner wrote:
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index eb2bf4629157..fc3c3cc9f689 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -242,6 +242,10 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
> >                       slab_flags_t flags,
> >                       unsigned int useroffset, unsigned int usersize,
> >                       void (*ctor)(void *));
> > +struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size,
> > +                                      unsigned int offset,
> > +                                      slab_flags_t flags,
> > +                                      void (*ctor)(void *));
>
> I wonder if there's a way to do this in a more generic way, we'd now have 3
> variants and neither supports everything (what about both rcu offset and
> usercopy?).

The "pass all arguments as a struct" pattern might not look too bad
(or alternatively, "pass all optional arguments as a struct"), as long
as it's fine for unused arguments to be zero-initialized? Like:

struct kcr_options {
    const char *name;
    unsigned int size;
    ...
};

struct kmem_cache *kmem_cache_create(struct kcr_options opt);

void blah() {
  kmem_cache_create((struct kcr_options){
    .name = "blah",
    .size = ...,
    ...
  });
}

I think maybe we can do this now that the kernel is C11?

But I guess if we want to allow leaving out the freeptr_offset
parameter, we'd have to have a flag to say whether the freeptr_offset
parameter value should be used... Maybe my proposal is too overly
fancy...