man > proc_buddyinfo(5)

proc_buddyinfo(5)                        File Formats Manual                       proc_buddyinfo(5)

NAME
       /proc/buddyinfo - memory fragmentation

DESCRIPTION
       /proc/buddyinfo
              This  file  contains information which is used for diagnosing memory fragmentation is‐
              sues.  Each line starts with the identification of the node and the name of  the  zone
              which together identify a memory region.  This is then followed by the count of avail‐
              able chunks of a certain order in which these zones are split.  The size in bytes of a
              certain order is given by the formula:

                  (2^order) * PAGE_SIZE

              The  binary  buddy allocator algorithm inside the kernel will split one chunk into two
              chunks of a smaller order (thus with half the size) or combine two  contiguous  chunks
              into one larger chunk of a higher order (thus with double the size) to satisfy alloca‐
              tion  requests and to counter memory fragmentation.  The order matches the column num‐
              ber, when starting to count at zero.

              For example on an x86-64 system:
         Node 0, zone     DMA     1    1    1    0    2    1    1    0    1    1    3
         Node 0, zone   DMA32    65   47    4   81   52   28   13   10    5    1  404
         Node 0, zone  Normal   216   55  189  101   84   38   37   27    5    3  587

              In this example, there is one node containing three zones and there are  11  different
              chunk  sizes.  If the page size is 4 kilobytes, then the first zone called DMA (on x86
              the first 16 megabyte of memory) has 1 chunk of 4 kilobytes (order  0)  available  and
              has 3 chunks of 4 megabytes (order 10) available.

              If the memory is heavily fragmented, the counters for higher order chunks will be zero
              and allocation of large contiguous areas will fail.

              Further information about the zones can be found in /proc/zoneinfo.

SEE ALSO
       proc(5)

Linux man-pages 6.7                          2023-08-15                            proc_buddyinfo(5)