====== Proc - Buddy Info file ======

External fragmentation is a problem under some workloads, and buddyinfo is a useful tool for helping diagnose these problems.  Buddyinfo will give you a clue as to how big an area you can safely allocate, or why a previous allocation failed.

<code bash>
cat /proc/buddyinfo

Node 0, zone      DMA      0      4      5      4      4      3 ...
Node 0, zone   Normal      1      0      0      1    101      8 ...
Node 0, zone  HighMem      2      0      0      1      1      0 ...
</code>

Each column represents the number of pages of a certain order which are available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE available in ZONE_NORMAL, etc... 

More information relevant to external fragmentation can be found in [[Proc:Page Type Info file|pagetypeinfo]].