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Lustre Debugging for Developers: Difference between revisions

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'''[[How is this facility used?]]'''
'''[[How is this facility used?]]'''


=Finding memory leaks=
=Finding memory leaks using ''leak_finder.pl''=


Memory leaks can occur in code when memory has been allocated and then not freed once it is no longer required. The ''leak_finder.pl'' program provides a way to find memory leaks.  To use this program, follow these steps:
Memory leaks can occur in code when memory has been allocated and then not freed once it is no longer required. The ''leak_finder.pl'' program provides a way to find memory leaks.   


1. Turn on debugging to make sure all malloc and free entries are collected by entering:
For details, see [http://wiki.lustre.org/manual/LustreManual18_HTML/LustreDebugging.html#50532482_pgfId-1291477 Section 23.2.4: ''Finding Memory Leaks''] in the [[Lustre Documentation|''Lustre Operations Manual'']].
 
sysctl -w lnet.debug=+malloc
 
2. Use ''lctl'' to dump the log into a user specified log file as shown in [[previous section]].
 
3. Run the leak finder on the contents of the log file by entering:
 
perl leak_finder.pl <ascii-logname>
 
The output is similar to:
 
:<pre>
; malloced  8bytes  at a3116744 called pathcopy
; (lprocfs_status.c:lprocfs_add_vars:80)
; freed      8bytes  at a3116744 called pathcopy
; (lprocfs_status.c:lprocfs_add_vars:80)
</pre>
 
The ''leak_finder.pl'' tool also displays any leaks that were found found:
 
Leak:32bytes allocated at a23a8fc  (service.c:ptlrpc_init_svc:144,debug file line 241)

Revision as of 12:20, 27 January 2010

Intro...

Adding Debugging to the Source Code

The debug infrastructure provides a number of macros that can be used in Lustre™ source code to aid in debugging or reporting serious errors.

To use these macros, you will need to set the DEBUG_SUBSYSTEM variable at the top of the file to do what?? as shown below: 

#define DEBUG_SUBSYSTEM S_PORTALS

A list of available macros with descriptions is provided in see Section 23.2.8: Adding Debugging to the Lustre Source Code in the Lustre Operations Manual.

Ptlrpc Request History ...Requesting a service history using prlrpc?

Each service maintains a request history, which can be useful for first occurrence troubleshooting.

Is ptlrpc an acronym?

[[PTLRPC An RPC protocol layered on LNET. This protocol deals with stateful servers and has exactly-once semantics and built in support for recovery.]]

prlrpc is listed as a subsystem in the Lustre Debug Messages section.

For more information about how to use prlrpc, see Section 23.5: Ptlrpc Request History in the Lustre Operations Manual.

Using lightweight tracing (LWT) for debugging

Lustre offers a lightweight tracing facility called LWT that can be useful for debugging difficult problems. It prints fixed size requests into a buffer and is much faster than LDEBUG.

LWT trace-based records that are dumped contain:

  • Current CPU
  • Process counter
  • Pointer to file
  • Pointer to line in the file
  • Four void * pointers

An lctl command dumps the logs to files.

How is this facility used?

Finding memory leaks using leak_finder.pl

Memory leaks can occur in code when memory has been allocated and then not freed once it is no longer required. The leak_finder.pl program provides a way to find memory leaks.

For details, see Section 23.2.4: Finding Memory Leaks in the Lustre Operations Manual.

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