Memtester output messages like:

"Allocated 61569920 bytes...trying mlock...failed:  insufficient resources."

are *NORMAL*.
According to the documentation, malloc errors mean that memtester is
encountering difficulty allocating the given amount of memory for
testing (presumably because it's in use). It keeps trying, reducing the
memory size (or trying a different block) until it is able to allocate
that memory block size to testing and proceed with its tests.
Multiple instances of memtester can be run in parallel to provide full
coverage of memory.