try_to_unmap_file( ) in non-linear memory region of the file

["Wang Yu" <wangyuict@xxxxxxxxx>]

Hi, all
When the mapping is non-linear, in try_to_unmap_file( ) we will have
the following codes:

	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
		if ((vma->vm_flags & VM_LOCKED) && !migration)
			continue;
		cursor = (unsigned long) vma->vm_private_data;
		if (cursor > max_nl_cursor)
			max_nl_cursor = cursor;
		cursor = vma->vm_end - vma->vm_start;
		if (cursor > max_nl_size)
			max_nl_size = cursor;
	}
	mapcount = page_mapcount(page);
	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
	if (max_nl_cursor == 0)
		max_nl_cursor = CLUSTER_SIZE;

	do {
		list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
						shared.vm_set.list) {
			if ((vma->vm_flags & VM_LOCKED) && !migration)
				continue;
			cursor = (unsigned long) vma->vm_private_data;
			while ( cursor < max_nl_cursor &&
				cursor < vma->vm_end - vma->vm_start) {
				try_to_unmap_cluster(cursor, &mapcount, vma);
				cursor += CLUSTER_SIZE;
				vma->vm_private_data = (void *) cursor;
				if ((int)mapcount <= 0)
					goto out;
			}
			vma->vm_private_data = (void *) max_nl_cursor;
		}
		cond_resched_lock(&mapping->i_mmap_lock);
		max_nl_cursor += CLUSTER_SIZE;
	} while (max_nl_cursor <= max_nl_size);
	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
		vma->vm_private_data = NULL;

What I want to know is what is the meaning of cursor and CLUSTER_SIZE?
and what does try_to_unmap_cluster want to do?
I am appreciated if someone will explain these codes in detail or give
me some documents about this?

Thanks!
-- 
National Research Center for Intelligent Computing Systems
Institute of Computing Technology, Chinese Academy of Sciences

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