Re: [PATCH v2 bpf] bpf: Replace bpf_map_kmalloc_node() with kmalloc_nolock() to allocate bpf_async_cb structures.

[Vlastimil Babka <vbabka@suse.cz>]

On 10/15/25 04:12, Alexei Starovoitov wrote:
> On Tue, Oct 14, 2025 at 6:59 PM Harry Yoo <harry.yoo@oracle.com> wrote:
>>
>> >
>> > Fixes: 6d78b4473cdb ("bpf: Tell memcg to use allow_spinning=false path in bpf_timer_init()")
>> > Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
>> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
>> > ---
>>
>> LGTM,
>> Acked-by: Harry Yoo <harry.yoo@oracle.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

>>
>> So we're losing benefit of batch-processing via kfree_rcu() and
>> instead using call_rcu(), and I guess it's fine since it's not very
>> performance critical
> 
> yes. Here freeing is not in critical path.
> 
>> so we don't have to make kfree_rcu() work with
>> objects that are allocated via kmalloc_nolock()?
> 
> Not quite :) It's on the todo list.
> Something like kfree_nolock_rcu() is needed, and
> also SLAB_TYPESAFE_BY_RCU-like and new SLAB_TYPESAFE_BY_SRCU_FAST flag.
> The plan for the upcoming merge window is to delete rcu tasks trace
> and replace with srcu_fast. It will clarify next steps.

I'm a bit afraid if this approach of stricly matching kmalloc_nolock() with
kfree_nolock() is going to be a neverending whack-a-mole. Let's see...