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 mem-
ory fragmentation issues. Each line starts with the identifica-
tion of the node and the name of the zone which together iden-
tify 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 kilo-
bytes, then the first zone called DMA (on x86 the first 16
megabyte of memory) has 1 chunk of 4 kilobytes (order 0) avail-
able and has 3 chunks of 4 megabytes (order 10) available.
If the memory is heavily fragmented, the counters for higher or-
der chunks will be zero and allocation of large contiguous areas
will fail.
Further information about the zones can be found in /proc/zone-
info.
SEE ALSO
proc(5)
Linux man-pages 6.7 2023-08-15 proc_buddyinfo(5)
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