desfree
Parameter
- Description
-
Specifies the preferred amount of memory to be free at all times on the system.
- Data Type
-
Unsigned integer
- Default
-
lotsfree
/ 2 - Range
-
The minimum value is 256 KB or 1/128th of physical memory, whichever is greater, expressed as pages using the page size returned by
getpagesize
.The maximum value is the number of physical memory pages. The maximum value should be no more than 15 percent of physical memory. The system does not enforce this range other than that described in the Validation section.
- Units
-
Pages
- Dynamic?
-
Yes, unless dynamic reconfiguration operations that add or delete memory occur. At that point, the value is reset to the value provided in
/etc/system.d/file
or calculated from the new physical memory value. - Validation
-
If
desfree
is greater thanlotsfree
,desfree
is set tolotsfree
/ 2. No message is displayed. - Implicit
-
The relationship of
lotsfree
being greater thandesfree
, which is greater thanminfree
, should be maintained at all times. - Side Effects
-
Several side effects can arise from increasing the value of this parameter. When the new value nears or exceeds the amount of available memory on the system, the following can occur:
-
Asynchronous I/O requests are not processed, unless available memory exceeds
desfree
. Increasing the value ofdesfree
can result in rejection of requests that otherwise would succeed. -
NFS asynchronous writes are executed as synchronous writes.
-
The swapper is awakened earlier, and the behavior of the swapper is biased towards more aggressive actions.
-
The system might not preload (prefault) as many executable pages as possible into the system. This side effect results in applications potentially running slower than they otherwise would.
-
- When to Change
-
For systems with relatively static workloads and large amounts of memory, lower this value. The minimum acceptable value is 256 KB, expressed as pages using the page size returned by
getpagesize
. - Commitment Level
-
Unstable