slab: simplify kmalloc_nolock()

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The kmalloc_nolock() implementation has several complications and
restrictions due to SLUB's cpu slab locking, lockless fastpath and
PREEMPT_RT differences. With cpu slab usage removed, we can simplify
things:

- relax the PREEMPT_RT context checks as they were before commit
  99a3e3a1cf ("slab: fix kmalloc_nolock() context check for
  PREEMPT_RT") and also reference the explanation comment in the page
  allocator

- the local_lock_cpu_slab() macros became unused, remove them

- we no longer need to set up lockdep classes on PREEMPT_RT

- we no longer need to annotate ___slab_alloc as NOKPROBE_SYMBOL
  since there's no lockless cpu freelist manipulation anymore

- __slab_alloc_node() can be called from kmalloc_nolock_noprof()
  unconditionally. It can also no longer return EBUSY. But trylock
  failures can still happen so retry with the larger bucket if the
  allocation fails for any reason.

Note that we still need __CMPXCHG_DOUBLE, because while it was removed
we don't use cmpxchg16b on cpu freelist anymore, we still use it on
slab freelist, and the alternative is slab_lock() which can be
interrupted by a nmi. Clarify the comment to mention it specifically.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Hao Li <hao.li@linux.dev>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

...

This commit is contained in:

Vlastimil Babka 2026-01-23 07:52:53 +01:00

parent ab2f752ac3

commit 073d5f1562

2 changed files with 29 additions and 116 deletions

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mm/slab.h

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144

mm/slub.c

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