How does memory fragmentation occur?

How does memory fragmentation occur?

External fragmentation arises when free memory is separated into small blocks and is interspersed by allocated memory. It is a weakness of certain storage allocation algorithms, when they fail to order memory used by programs efficiently. The memory allocator can use this free block of memory for future allocations.

Is memory fragmentation still an issue?

In general c++ programing there is no problem with memory fragmentation. You always see the virtual memory and you always allocate contiguous virtual memory chunks. The only thing that you can notice that the sequentially allocated chunks are not necessarily adjacent in memory.

How is memory fragmentation related to compaction of memory?

Memory fragmentation is a condition when the system is running low on physically contiguous chunks, which makes impossible physically contiguous allocations required by some device drivers and other kernel functions. Compaction is a method of reversing memory fragmentation.

How can you tell if memory fragmentation is a problem?

The only way to confirm the impact of memory fragmentation on system’s performance is by observing compaction-related kernel stacks by one of available stack sampling techniques. When your problem is compaction, you will see something like this:

Is there a way to reduce memory fragmentation?

In many cases, memory fragmentation can be reduced by tweaking VM parameters. Of course, as with any low-level change, you really need to know what you are doing, so it’s best to get a consult from a Linux expert, or from Oracle support in an SR (and do some good testing).

How is virtual memory used to hide memory fragmentation?

Physical memory addresses are mapped to virtual addresses, which means that virtual memory can “hide” memory fragmentation and produce a contiguous range of virtual addresses without physically moving the contents of the memory pages