Does the page & dentry cache reset on low memory?

In low-memory situations, does the page & dentry cache reset?
If a library is in use by a process, does that necessarily mean it will stay in cache (at least the read-only pages) even in low memory situations?

Also, as the entire purpose of the page cache is to be quicker the disk, I assume it will not use swap. Can the dentry cache use swap?

Thanks