Re: mm: percpu: increase PERCPU_MODULE_RESERVE to avoid allocation failure

[Suren Baghdasaryan <surenb@google.com>]

On Wed, Apr 23, 2025 at 8:12 AM Tejun Heo <tj@kernel.org> wrote:
>
> On Tue, Apr 22, 2025 at 05:19:31PM -0700, Suren Baghdasaryan wrote:
> ...
> > Allocating this reserved area dynamically would be ideal. OTOH this
> > change increases the area size from 64kb to 128kb. Don't know how much
> > effort we should put into it.
>
> The easiest solution would be switching the modules to use alloc_percpu()
> instead of declaring per-cpu variables statically. I couldn't think of a
> better way to support static percpu variables in modules and still can't,
> but there aren't noticeable downsides to using dynamically allocated percpu
> variables, so if you have several bytes here and there, sure, declare them
> statically, but for anything chunky, please use dynamic allocations.

In case of allocation tags, we are trying to minimize performance
overhead as much as possible and allocating their per-cpu counters at
compile time is in line with that goal. I'll check how much overhead
dynamic allocation would add but it won't be zero.

>
> Thanks.
>
> --
> tejun