Re: [PATCH v4 07/12] mm: enable lazy_mmu sections to nest

[Alexander Gordeev <agordeev@xxxxxxxxxxxxx>]

On Thu, Oct 30, 2025 at 11:28:53AM +0100, Kevin Brodsky wrote:
> On 29/10/2025 17:41, Alexander Gordeev wrote:
> > On Wed, Oct 29, 2025 at 10:09:04AM +0000, Kevin Brodsky wrote:
> >
> > Hi Kevin,
> >
> >> +#ifdef CONFIG_ARCH_HAS_LAZY_MMU_MODE
> >> +static inline bool in_lazy_mmu_mode(void)
> >> +{
> >> +  return current->lazy_mmu_state.active;
> > Whether (nesting_level > 0) is more correct check?
> > Otherwise, it returns false while in paused mode.
> 
> That's exactly the intention. Lazy MMU is disabled while paused. The
> users of that helper want to know if lazy MMU is currently enabled (to
> decide whether to batch updates for instance); whether this is because
> we are paused or not in any lazy_mmu section (nesting_level == 0) makes
> no difference.
> 
> > May be check both nesting_level and active and also introduce
> > in_lazy_mmu_paused_mode() right away to avoid any confusion?
> 
> Can you think of any situation where a caller would specifically want to
> know that lazy MMU is paused?

I thought I do, but in_lazy_mmu_mode() alone works just fine,
as you described (at least for now).

> - Kevin

Thanks!