Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs

["David Hildenbrand (Arm)" <david@kernel.org>]

On 11/6/26 13:07, Lorenzo Stoakes (ARM) wrote:
> On reflection, I think this would be better implemented as something like:
> 
> static void collapse_scan_mm_slot(unsigned int progress_max, ...)
> {
> 	unsigned int long lock_start = jiffies;
> 	...
>   	for_each_vma(vmi, vma) {
> 		...
>                 if (time_after(jiffies, lock_start) && mmap_lock_is_contended(mm)) {
>                         mmap_read_unlock(mm);
>                         cond_resched();
>                         mmap_read_lock(mm);
>                         lock_start = jiffies;
>                         vma_iter_set(&vmi, mm_slot->address);
>                         continue;
>                 }
> 	}
> }
> 
> Which avoids magic numbers, and means if we hold the lock for 1-10ms (depending
> on HZ), which is a long time in the kernel to hold a lock, AND the lock is
> contended, we drop/reacquire.

That approach indeed sounds better to me regarding lock contention.

-- 
Cheers,

David