Re: [PATCH bpf-next] bpf: Add a retry after refilling the free list when unit_alloc() fails

[Changwoo Min <changwoo@igalia.com>]

Hello Kumar,

On 25. 2. 13. 18:05, Kumar Kartikeya Dwivedi wrote:
> On Thu, 13 Feb 2025 at 09:42, Changwoo Min <changwoo@igalia.com> wrote:
>>
>> Hello Song,
>>
>> Thank you for the review!
>>
>> On 25. 2. 13. 03:33, Song Liu wrote:
>>> On Wed, Feb 12, 2025 at 12:49 AM Changwoo Min <changwoo@igalia.com> wrote:
>>>>
>>>> When there is no entry in the free list (c->free_llist), unit_alloc()
>>>> fails even when there is available memory in the system, causing allocation
>>>> failure in various BPF calls -- such as bpf_mem_alloc() and
>>>> bpf_cpumask_create().
>>>>
>>>> Such allocation failure can happen, especially when a BPF program tries many
>>>> allocations -- more than a delta between high and low watermarks -- in an
>>>> IRQ-disabled context.
>>>
>>> Can we add a selftests for this scenario?
>>
>> It would be a bit tricky to create an IRQ-disabled case in a BPF
>> program. However, I think it will be possible to reproduce the
>> allocation failure issue when allocating sufficiently enough
>> small allocations.
> 
> You can also make use of recently introduced
> bpf_local_irq_{save,restore} in the selftest.

Thank you for the suggestion. I will try it out.

Regards,
Changwoo Min