[PATCH v4 00/17] slab: add struct kmem_cache_args

[Christian Brauner <brauner@kernel.org>]

Hey,

This is v4 which allows NULL to be passed in the struct kmem_cache_args
argument of kmem_cache_create() and substitutes default parameters in
this case.

As discussed last week the various kmem_cache_*() functions should be
replaced by a unified function that is based around a struct, with only
the basic parameters passed separately.

Vlastimil already said that he would like to keep core parameters out
of the struct: name, object size, and flags. I personally don't care
much and would not object to moving everything into the struct but
that's a matter of taste and I yield that decision power to the
maintainer.

In the first version I pointed out that the choice of name is somewhat
forced as kmem_cache_create() is taken and the only way to reuse it
would be to replace all users in one go. Or to do a global
sed/kmem_cache_create()/kmem_cache_create2()/g. And then introduce
kmem_cache_setup(). That doesn't strike me as a viable option.

If we really cared about the *_create() suffix then an alternative might
be to do a sed/kmem_cache_setup()/kmem_cache_create()/g after every user
in the kernel is ported. I honestly don't think that's worth it but I
wanted to at least mention it to highlight the fact that this might lead
to a naming compromise.

However, I came up with an alternative using _Generic() to create a
compatibility layer that will call the correct variant of
kmem_cache_create() depending on whether struct kmem_cache_args is
passed or not. That compatibility layer can stay in place until we
updated all calls to be based on struct kmem_cache_args.

From a cursory grep (and not excluding Documentation mentions) we will
have to replace 44 kmem_cache_create_usercopy() calls and about 463
kmem_cache_create() calls which makes for a bit above 500 calls to port
to kmem_cache_setup(). That'll probably be good work for people getting
into kernel development.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
Changes in v4:
- Allow NULL to be passed in the struct kmem_cache_args argument of
  kmem_cache_create() and use default parameters in this case.
- Link to v3: https://lore.kernel.org/r/20240904-work-kmem_cache_args-v3-0-05db2179a8c2@kernel.org

Changes in v3:
- Reworded some commit messages.
- Picked up various RvBs.
- Added two patches to make two functions static inline.
- Link to v2: https://lore.kernel.org/r/20240903-work-kmem_cache_args-v2-0-76f97e9a4560@kernel.org

Changes in v2:
- Remove kmem_cache_setup() and add a compatibility layer built around
  _Generic() so that we can keep the kmem_cache_create() name and type
  switch on the third argument to either call __kmem_cache_create() or
  __kmem_cache_create_args().
- Link to v1: https://lore.kernel.org/r/20240902-work-kmem_cache_args-v1-0-27d05bc05128@kernel.org

---
Christian Brauner (17):
      slab: s/__kmem_cache_create/do_kmem_cache_create/g
      slab: add struct kmem_cache_args
      slab: port kmem_cache_create() to struct kmem_cache_args
      slab: port kmem_cache_create_rcu() to struct kmem_cache_args
      slab: port kmem_cache_create_usercopy() to struct kmem_cache_args
      slab: pass struct kmem_cache_args to create_cache()
      slab: pull kmem_cache_open() into do_kmem_cache_create()
      slab: pass struct kmem_cache_args to do_kmem_cache_create()
      slab: remove rcu_freeptr_offset from struct kmem_cache
      slab: port KMEM_CACHE() to struct kmem_cache_args
      slab: port KMEM_CACHE_USERCOPY() to struct kmem_cache_args
      slab: create kmem_cache_create() compatibility layer
      file: port to struct kmem_cache_args
      slab: remove kmem_cache_create_rcu()
      slab: make kmem_cache_create_usercopy() static inline
      slab: make __kmem_cache_create() static inline
      io_uring: port to struct kmem_cache_args

 fs/file_table.c      |  11 ++-
 include/linux/slab.h | 130 +++++++++++++++++++++++++++------
 io_uring/io_uring.c  |  14 ++--
 mm/slab.h            |   6 +-
 mm/slab_common.c     | 197 +++++++++++----------------------------------------
 mm/slub.c            | 162 +++++++++++++++++++++---------------------
 6 files changed, 250 insertions(+), 270 deletions(-)
---
base-commit: 6e016babce7c845ed015da25c7a097fa3482d95a
change-id: 20240902-work-kmem_cache_args-e9760972c7d4