Saslauthd constantly increasing memory use, solved by enabling caching. Why?

[Mark London <mrl@xxxxxxxxxxxx>]

Hi - On RHEL 6, with the latest updates, I have SASLAUTHD configured to 
use PAM authentication.  I'm also running SSSD. U sing this 
configuration, the SASLAUTHD processes would gradually increase memory 
usage.  After running for several days, each process was using up about 
680M.  Are there any known memory leaks when using PAM?  I've found 
posts on the web from people complaining about PAM memory leaks, but am 
not sure they still exists.  In any event, I'm also experiencing that 
about once a week, SASLAUTHD starts recording time out errors when 
trying to contact SSSD, i.e. "pam_sss(imap:auth): Request to sssd 
failed. Timer expired."   I decided to enable SASLAUTHD caching with the 
-c flag, and was surprised to discover that the SASLAUTHD processes no 
longer use up significant memory (i.e. they are now using < 10M)!  Can 
anyone explain this behavior?  Thanks. - Mark