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<literal>vnlru</literal> flushes and frees vnodes when the system hits the <varname>kern.maxvnodes</varname> limit. This kernel thread sits mostly idle, and only activates when there is a huge amount of RAM and users are accessing tens of thousands of tiny files.
What do the various memory states displayed by <command>top</command> mean?
<literal>Active</literal>: pages recently statistically used.
<literal>Inactive</literal>: pages recently statistically unused.
<literal>Laundry</literal>: pages recently statistically unused but known to be dirty, that is, whose contents needs to be paged out before they can be reused.
<literal>Free</literal>: pages without data content, which can be immediately reused.
<literal>Wired</literal>: pages that are fixed into memory, usually for kernel purposes, but also sometimes for special use in processes.
Pages are most often written to disk (sort of a VM sync) when they are in the laundry state, but active or inactive pages can also be synced. This depends upon the CPU tracking of the modified bit being available, and in certain situations there can be an advantage for a block of VM pages to be synced, regardless of the queue they belong to. In most common cases, it is best to think of the laundry queue as a queue of relatively unused pages that might or might not be in the process of being written to disk. The inactive queue contains a mix of clean and dirty pages; clean pages near the head of the queue are reclaimed immediately to alleviate a free page shortage, and dirty pages are moved to the laundry queue for deferred processing.
There are some other flags (e.g., busy flag or busy count) that might modify some of the described rules.
How much free memory is available?
There are a couple of kinds of <quote>free memory</quote>. The most common is the amount of memory immediately available without reclaiming memory already in use. That is the size of the free pages queue plus some other reserved pages. This amount is exported by the <literal>vm.stats.vm.v_free_count</literal> <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>, shown, for instance, by <citerefentry><refentrytitle>top</refentrytitle><manvolnum>1</manvolnum></citerefentry>. Another kind of <quote>free memory</quote> is the total amount of virtual memory available to userland processes, which depends on the sum of swap space and usable memory. Other kinds of <quote>free memory</quote> descriptions are also possible, but it is relatively useless to define these, but rather it is important to make sure that the paging rate is kept low, and to avoid running out of swap space.

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