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NAME | DESCRIPTION | SEE ALSO | COLOPHON |
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proc_buddyinfo(5) File Formats Manual proc_buddyinfo(5)
/proc/buddyinfo - memory fragmentation
/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.
proc(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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Linux man-pages 6.15 2025-05-17 proc_buddyinfo(5)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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