proc_buddyinfo(5) — Linux manual page

NAME | DESCRIPTION | SEE ALSO | COLOPHON

proc_buddyinfo(5)          File Formats Manual         proc_buddyinfo(5)

NAME         top

       /proc/buddyinfo - memory fragmentation

DESCRIPTION         top

       /proc/buddyinfo
              This file contains information which is used for
              diagnosing memory fragmentation issues.  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 available 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 allocation requests and to counter
              memory fragmentation.  The order matches the column
              number, 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         top

       proc(5)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02              proc_buddyinfo(5)