[thirdparty/man-pages.git] / man5 / proc_buddyinfo.5

.\" Copyright (C) 1994, 1995, Daniel Quinlan <quinlan@yggdrasil.com>
.\" Copyright (C) 2002-2008, 2017, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright (C) 2023, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: GPL-3.0-or-later
.\"
.TH proc_buddyinfo 5 (date) "Linux man-pages (unreleased)"
.SH NAME
/proc/buddyinfo \- memory fragmentation
.SH DESCRIPTION
.TP
.I /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:
.IP
.in +4n
.EX
(2\[ha]order)\ *\ PAGE_SIZE
.EE
.in
.IP
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.
.IP
For example on an x86-64 system:
.RS -12
.EX
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
.EE
.RE
.IP
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
.I 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.
.IP
If the memory is heavily fragmented, the counters for higher
order chunks will be zero and allocation of large contiguous areas
will fail.
.IP
Further information about the zones can be found in
.IR /proc/zoneinfo .
.SH SEE ALSO
.BR proc (5)
Commit	Line	Data
070a30bc AC	1	.\" Copyright (C) 1994, 1995, Daniel Quinlan <quinlan@yggdrasil.com>
	2	.\" Copyright (C) 2002-2008, 2017, Michael Kerrisk <mtk.manpages@gmail.com>
	3	.\" Copyright (C) 2023, Alejandro Colomar <alx@kernel.org>
	4	.\"
	5	.\" SPDX-License-Identifier: GPL-3.0-or-later
	6	.\"
	7	.TH proc_buddyinfo 5 (date) "Linux man-pages (unreleased)"
	8	.SH NAME
	9	/proc/buddyinfo \- memory fragmentation
	10	.SH DESCRIPTION
	11	.TP
	12	.I /proc/buddyinfo
	13	This file contains information which is used for diagnosing memory
	14	fragmentation issues.
	15	Each line starts with the identification of the node and the name
	16	of the zone which together identify a memory region.
	17	This is then
	18	followed by the count of available chunks of a certain order in
	19	which these zones are split.
	20	The size in bytes of a certain order is given by the formula:
	21	.IP
	22	.in +4n
	23	.EX
	24	(2\[ha]order)\ *\ PAGE_SIZE
	25	.EE
	26	.in
	27	.IP
	28	The binary buddy allocator algorithm inside the kernel will split
	29	one chunk into two chunks of a smaller order (thus with half the
	30	size) or combine two contiguous chunks into one larger chunk of
	31	a higher order (thus with double the size) to satisfy allocation
	32	requests and to counter memory fragmentation.
	33	The order matches the column number, when starting to count at zero.
	34	.IP
	35	For example on an x86-64 system:
	36	.RS -12
	37	.EX
	38	Node 0, zone DMA 1 1 1 0 2 1 1 0 1 1 3
	39	Node 0, zone DMA32 65 47 4 81 52 28 13 10 5 1 404
	40	Node 0, zone Normal 216 55 189 101 84 38 37 27 5 3 587
	41	.EE
	42	.RE
	43	.IP
	44	In this example, there is one node containing three zones and there
	45	are 11 different chunk sizes.
	46	If the page size is 4 kilobytes, then the first zone called
	47	.I DMA
	48	(on x86 the first 16 megabyte of memory) has 1 chunk of 4 kilobytes
	49	(order 0) available and has 3 chunks of 4 megabytes (order 10) available.
	50	.IP
	51	If the memory is heavily fragmented, the counters for higher
	52	order chunks will be zero and allocation of large contiguous areas
	53	will fail.
	54	.IP
	55	Further information about the zones can be found in
	56	.IR /proc/zoneinfo .
	57	.SH SEE ALSO
	58	.BR proc (5)