Re: [PATCH v2 1/1] mm/vmalloc: remove preempt_disable/enable when do preloading

[Daniel Wagner]

On 10/11/19 8:15 PM, Sebastian Andrzej Siewior wrote:
> On 2019-10-11 00:33:18 [+0200], Uladzislau Rezki (Sony) wrote:
> > Get rid of preempt_disable() and preempt_enable() when the
> > preload is done for splitting purpose. The reason is that
> > calling spin_lock() with disabled preemtion is forbidden in
> > CONFIG_PREEMPT_RT kernel.
> >
> > Therefore, we do not guarantee that a CPU is preloaded, instead
> > we minimize the case when it is not with this change.
> >
> > For example i run the special test case that follows the preload
> > pattern and path. 20 "unbind" threads run it and each does
> > 1000000 allocations. Only 3.5 times among 1000000 a CPU was
> > not preloaded. So it can happen but the number is negligible.
> >
> > V1 -> V2:
> >    - move __this_cpu_cmpxchg check when spin_lock is taken,
> >      as proposed by Andrew Morton
> >    - add more explanation in regard of preloading
> >    - adjust and move some comments
> >
> > Fixes: 82dd23e84be3 ("mm/vmalloc.c: preload a CPU with one object for split purpose")
> > Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
>
> Acked-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

Acked-by: Daniel Wagner <dwagner@xxxxxxx>