Performance Tuning -Part 4

                   










 





 

5.1 laptop mode

Laptop Mode is an umbrella setting designed to increase battery life in lap-tops. By enablinglaptop mode the VM makes decisions regarding the write-out of pages in such a way as toattempt to minimize high power operations. Specifically, enabling laptop mode does thefollowing:

•

Modifies the behavior of kswapd to allow more pages to dirty before swapping

•

 

Modifies the behavior of pdflush to allow more buffers to be dirty before writingthem back to disk

 

Coordinates the activities of kswapd and pdflush such that they write to disk whenthe disk is active to avoid unneeded disk spin up activity, which wastes batterypower

 

 

5.2 overcommit memory

Overcommit memory is a value which sets the general kernel policy toward granting memoryallocations. If the value in this file is 0, then the kernel will check to see if there is enoughmemory free to grant a memory request to a malloc call from an application. If there is enoughmemory then the request is granted. Otherwise it is denied and an error code is returned tothe application. If the setting in this file is 1, the kernel will allow all memory allocations,regardless of the current memory allocation state. If the value is set to 2, then the kernel willgrant allocations above the amount of physical ram and swap in the system, as defined by theovercommit ratio value (defined below). Enabling this feature can be somewhat helpful inenvironments which allocate large amounts of memory expecting worst case scenarios, but donot use it all.You can check to see how much memory you are using and how much you have free by usingthe free command. Run the free command when your system is running at the bestperformance. This will ensure that all applications have already taken their memory.In the following output, the system only uses 110 MB of 256 MB of total swap.