Merge branch 'replace-page_frag-with-page_frag_cache-part-1'

Yunsheng Lin says:

====================
Replace page_frag with page_frag_cache (Part-1)

This is part 1 of "Replace page_frag with page_frag_cache",
which mainly contain refactoring and optimization for the
implementation of page_frag API before the replacing.

As the discussion in [1], it would be better to target net-next
tree to get more testing as all the callers page_frag API are
in networking, and the chance of conflicting with MM tree seems
low as implementation of page_frag API seems quite self-contained.

After [2], there are still two implementations for page frag:

1. mm/page_alloc.c: net stack seems to be using it in the
   rx part with 'struct page_frag_cache' and the main API
   being page_frag_alloc_align().
2. net/core/sock.c: net stack seems to be using it in the
   tx part with 'struct page_frag' and the main API being
   skb_page_frag_refill().

This patchset tries to unfiy the page frag implementation
by replacing page_frag with page_frag_cache for sk_page_frag()
first. net_high_order_alloc_disable_key for the implementation
in net/core/sock.c doesn't seems matter that much now as pcp
is also supported for high-order pages:
commit 44042b449872 ("mm/page_alloc: allow high-order pages to
be stored on the per-cpu lists")

As the related change is mostly related to networking, so
targeting the net-next. And will try to replace the rest
of page_frag in the follow patchset.

After this patchset:
1. Unify the page frag implementation by taking the best out of
   two the existing implementations: we are able to save some space
   for the 'page_frag_cache' API user, and avoid 'get_page()' for
   the old 'page_frag' API user.
2. Future bugfix and performance can be done in one place, hence
   improving maintainability of page_frag's implementation.

Kernel Image changing:
    Linux Kernel   total |      text      data        bss
    ------------------------------------------------------
    after     45250307 |   27274279   17209996     766032
    before    45254134 |   27278118   17209984     766032
    delta        -3827 |      -3839        +12         +0

1. https://lore.kernel.org/all/add10dd4-7f5d-4aa1-aa04-767590f944e0@redhat.com/
2. https://lore.kernel.org/all/20240228093013.8263-1-linyunsheng@huawei.com/
====================

Link: https://patch.msgid.link/20241028115343.3405838-1-linyunsheng@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>