> echo 3 > /proc/PID/clear_refs
Any other value written to /proc/PID/clear_refs will have no effect.
+To reset the peak resident set size ("high water mark") to the process's
+current value:
+ > echo 5 > /proc/PID/clear_refs
+
The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
using /proc/kpageflags and number of times a page is mapped using
/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.