[PATCH net-next v8 0/2] Abstract page from net stack

[Mina Almasry <almasrymina@google.com>]

Changes in v8:
- Moved back skb_add_rx_frag_netmem to .c file (Paolo).
- Applied Paolo's Acked-by.

-----------

Changes in v7;
- Addressed comments from Paolo.
  - Moved skb_add_rx_frag* to header file.
  - Moved kcmsock.c check.

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Changes in v6:
- Non-RFC as net-next opened.
- static_assert skb_frag_t compatibility with bio_vec.

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Changes in RFC v5:
- RFC due to merge window
- Changed netmem to __bitwise unsigned long.

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Changes in v4:
- Forked off the trivial fixes to skb_frag_t field access to their own
  patches and changed this to RFC that depends on these fixes:

https://lore.kernel.org/netdev/20240102205905.793738-1-almasrymina@google.com/T/#u
https://lore.kernel.org/netdev/20240102205959.794513-1-almasrymina@google.com/T/#u

- Use an empty struct for netmem instead of void* __bitwise as that's
  not a correct use of __bitwise.

-----------

Changes in v3:

- Replaced the struct netmem union with an opaque netmem_ref type.
- Added func docs to the netmem helpers and type.
- Renamed the skb_frag_t fields since it's no longer a bio_vec

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Changes in v2:
- Reverted changes to the page_pool. The page pool now retains the same
  API, so that we don't have to touch many existing drivers. The devmem
  TCP series will include the changes to the page pool.

- Addressed comments.

This series is a prerequisite to the devmem TCP series. For a full
snapshot of the code which includes these changes, feel free to check:

https://github.com/mina/linux/commits/tcpdevmem-rfcv5/

-----------

Currently these components in the net stack use the struct page
directly:

1. Drivers.
2. Page pool.
3. skb_frag_t.

To add support for new (non struct page) memory types to the net stack, we
must first abstract the current memory type.

Originally the plan was to reuse struct page* for the new memory types,
and to set the LSB on the page* to indicate it's not really a page.
However, for safe compiler type checking we need to introduce a new type.

struct netmem is introduced to abstract the underlying memory type.
Currently it's a no-op abstraction that is always a struct page underneath.
In parallel there is an undergoing effort to add support for devmem to the
net stack:

https://lore.kernel.org/netdev/20231208005250.2910004-1-almasrymina@google.com/

Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>

Mina Almasry (2):
  net: introduce abstraction for network memory
  net: add netmem to skb_frag_t

 include/linux/skbuff.h | 100 +++++++++++++++++++++++++++++------------
 include/net/netmem.h   |  41 +++++++++++++++++
 net/core/skbuff.c      |  34 +++++++++++---
 net/kcm/kcmsock.c      |   7 +--
 4 files changed, 143 insertions(+), 39 deletions(-)
 create mode 100644 include/net/netmem.h

-- 
2.43.0.687.g38aa6559b0-goog