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

[Lorenzo Stoakes (ARM)]

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.

--
Cheers, Lorenzo