IBM AIX Continuous Availability Features - IBM Redbooks

[00800] 00000400
[01000] 00000400
[02000] 00000400
[04000] 00000400
[08000] 00000400
Ratio of memory to declare a memory leak: 0x400(1024)/0x400(1024)
Outstanding memory allocations to declare a memory leak: -1
Deferred page reclamation count (-1 == when necessary): 16384
Minimum allocation size to force a record for: 1048576
Note: The bosdebug -M command sets all the frequencies for alloc.xmdbg at maximal level
except for “promotion settings” which are all set to zero (0). A reboot is required in order for
bosdebug to take effect.
3.9.4 XMDBG tunables affected by error check level
As previously mentioned, xmalloc RTEC features are activated for a given allocation based
on probabilities. The errctrl command that controls the tunables takes the probability of
application (frequency) as an argument.
In AIX V6.1, the user can set the probability of a check being performed by specifying the
frequency of a tunable as a number between 0 and 1024. This is the number of times out of
the base frequency (1024) that the technique is to be applied by xmalloc. For example, to
request 50%, the user specifies a frequency of 512.
Frequencies can be input as decimal or hex numbers, so 50% can be specified as 0x200. As
a convenient alternative, the frequency can be expressed as a percentage. To do this, the
user specifies a number between 0 and 100 followed by the percent (%) sign. The following
sections detail the RTEC tunables for the xmalloc.xmdbg component.
Keep an allocation record
This option sets the frequency of keeping a record for an allocation. Records are also kept if
any other debug technique is applied, so the percentage of allocations with a record may be
considerably larger than this number would otherwise indicate.
The allocation record contains a three-level stack trace-back of the xmalloc() and xmfree()
callers, as well as other debug information about the allocated memory. The presence of a
record is a minimum requirement for xmalloc run time error checking.
errctrl -c alloc.xmdbg alloc_record=
Ruin storage
This option sets the frequency at which xmalloc() will return storage that is filled with a “ruin”
pattern. This helps catch errors with un-initialized storage, because a caller with bugs is more
likely to crash when using the ruined storage. Note that xmalloc() does not perform any
explicit checks when this technique is employed. The ruined data will contain 0x66 in every
allocated byte on allocation, and 0x77 in every previously allocated byte after being freed.
errctrl -c alloc.xmdbg ruin_all=
Check for overwrites in small allocations
This is one of the three options that affect the frequency of trailers. There are two options that
deal with trailers, and a third option deals with compatibility with previous versions of AIX.
This option is specific for allocations that are less than half a page. A trailer is written
Chapter 3. AIX advanced continuous availability tools and features 131