[Samba] Winbind process stuck at 100% after changing use_mmap to no

[Alex Crow]

Hi,

We've had a strange issue after following the recommendations at 
https://wiki.samba.org/index.php/Ping_pong, particularly the part about 
mmap coherence. We are running CTDB/Samba over a MooseFS clustered FS, 
and we'd not done the ping-pong before. After finding that the mmap 
coherence test did not pass, we changed "use mmap" to "no" in smb.conf.

This morning as users began to access their drives and profiles, 
performance tanked to such a degree that most people could not complete 
loading profiles and even where successful, windows drive mappings were 
taking minutes to complete per share.

When looking at the active CTDB servers, on each a single Winbindd 
process was taking up 100% of CPU. After reverting the "use_mmap" to 
yes, performance returned completely to normal.

We found this very odd as this is a recommended setting according to the 
page above.

Here are package versions:

Installed Packages
Name        : samba
Arch        : x86_64
Version     : 4.2.10
Release     : 6.el7_2
Size        : 1.8 M
Repo        : installed
 From repo   : updates
Summary     : Server and Client software to interoperate with Windows 
machines
URL         : http://www.samba.org/
Licence     : GPLv3+ and LGPLv3+
Description : Samba is the standard Windows interoperability suite of 
programs for Linux and Unix.

Installed Packages
Name        : ctdb
Arch        : x86_64
Version     : 4.2.10
Release     : 6.el7_2
Size        : 1.2 M
Repo        : installed
 From repo   : updates
Summary     : A Clustered Database based on Samba's Trivial Database (TDB)
URL         : http://www.samba.org/
Licence     : GPLv3+ and LGPLv3+
Description : CTDB is a cluster implementation of the TDB database used 
by Samba and other
             : projects to store temporary data. If an application is 
already using TDB for
             : temporary data it is very easy to convert that 
application to be cluster aware
             : and use CTDB instead.

Linux zearing.ifa.net 3.10.0-327.18.2.el7.x86_64 #1 SMP Thu May 12 
11:03:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Best regards

Alex
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