1.. _page_owner:
2
3==================================================
4page owner: Tracking about who allocated each page
5==================================================
6
7Introduction
8============
9
10page owner is for the tracking about who allocated each page.
11It can be used to debug memory leak or to find a memory hogger.
12When allocation happens, information about allocation such as call stack
13and order of pages is stored into certain storage for each page.
14When we need to know about status of all pages, we can get and analyze
15this information.
16
17Although we already have tracepoint for tracing page allocation/free,
18using it for analyzing who allocate each page is rather complex. We need
19to enlarge the trace buffer for preventing overlapping until userspace
20program launched. And, launched program continually dump out the trace
21buffer for later analysis and it would change system behaviour with more
22possibility rather than just keeping it in memory, so bad for debugging.
23
24page owner can also be used for various purposes. For example, accurate
25fragmentation statistics can be obtained through gfp flag information of
26each page. It is already implemented and activated if page owner is
27enabled. Other usages are more than welcome.
28
29page owner is disabled by default. So, if you'd like to use it, you need
30to add "page_owner=on" to your boot cmdline. If the kernel is built
31with page owner and page owner is disabled in runtime due to not enabling
32boot option, runtime overhead is marginal. If disabled in runtime, it
33doesn't require memory to store owner information, so there is no runtime
34memory overhead. And, page owner inserts just two unlikely branches into
35the page allocator hotpath and if not enabled, then allocation is done
36like as the kernel without page owner. These two unlikely branches should
37not affect to allocation performance, especially if the static keys jump
38label patching functionality is available. Following is the kernel's code
39size change due to this facility.
40
41Although enabling page owner increases kernel size by several kilobytes,
42most of this code is outside page allocator and its hot path. Building
43the kernel with page owner and turning it on if needed would be great
44option to debug kernel memory problem.
45
46There is one notice that is caused by implementation detail. page owner
47stores information into the memory from struct page extension. This memory
48is initialized some time later than that page allocator starts in sparse
49memory system, so, until initialization, many pages can be allocated and
50they would have no owner information. To fix it up, these early allocated
51pages are investigated and marked as allocated in initialization phase.
52Although it doesn't mean that they have the right owner information,
53at least, we can tell whether the page is allocated or not,
54more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages
55are catched and marked, although they are mostly allocated from struct
56page extension feature. Anyway, after that, no page is left in
57un-tracking state.
58
59Usage
60=====
61
621) Build user-space helper::
63
64	cd tools/mm
65	make page_owner_sort
66
672) Enable page owner: add "page_owner=on" to boot cmdline.
68
693) Do the job that you want to debug.
70
714) Analyze information from page owner::
72
73	cat /sys/kernel/debug/page_owner > page_owner_full.txt
74	./page_owner_sort page_owner_full.txt sorted_page_owner.txt
75
76   The general output of ``page_owner_full.txt`` is as follows::
77
78	Page allocated via order XXX, ...
79	PFN XXX ...
80	// Detailed stack
81
82	Page allocated via order XXX, ...
83	PFN XXX ...
84	// Detailed stack
85    By default, it will do full pfn dump, to start with a given pfn,
86    page_owner supports fseek.
87
88    FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
89    fseek(fp, pfn_start, SEEK_SET);
90
91   The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows
92   in buf, uses regexp to extract the page order value, counts the times
93   and pages of buf, and finally sorts them according to the parameter(s).
94
95   See the result about who allocated each page
96   in the ``sorted_page_owner.txt``. General output::
97
98	XXX times, XXX pages:
99	Page allocated via order XXX, ...
100	// Detailed stack
101
102   By default, ``page_owner_sort`` is sorted according to the times of buf.
103   If you want to sort by the page nums of buf, use the ``-m`` parameter.
104   The detailed parameters are:
105
106   fundamental function::
107
108	Sort:
109		-a		Sort by memory allocation time.
110		-m		Sort by total memory.
111		-p		Sort by pid.
112		-P		Sort by tgid.
113		-n		Sort by task command name.
114		-r		Sort by memory release time.
115		-s		Sort by stack trace.
116		-t		Sort by times (default).
117		--sort <order>	Specify sorting order.  Sorting syntax is [+|-]key[,[+|-]key[,...]].
118				Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is
119				optional since default direction is increasing numerical or lexicographic
120				order. Mixed use of abbreviated and complete-form of keys is allowed.
121
122		Examples:
123				./page_owner_sort <input> <output> --sort=n,+pid,-tgid
124				./page_owner_sort <input> <output> --sort=at
125
126   additional function::
127
128	Cull:
129		--cull <rules>
130				Specify culling rules.Culling syntax is key[,key[,...]].Choose a
131				multi-letter key from the **STANDARD FORMAT SPECIFIERS** section.
132
133		<rules> is a single argument in the form of a comma-separated list,
134		which offers a way to specify individual culling rules.  The recognized
135		keywords are described in the **STANDARD FORMAT SPECIFIERS** section below.
136		<rules> can be specified by the sequence of keys k1,k2, ..., as described in
137		the STANDARD SORT KEYS section below. Mixed use of abbreviated and
138		complete-form of keys is allowed.
139
140		Examples:
141				./page_owner_sort <input> <output> --cull=stacktrace
142				./page_owner_sort <input> <output> --cull=st,pid,name
143				./page_owner_sort <input> <output> --cull=n,f
144
145	Filter:
146		-f		Filter out the information of blocks whose memory has been released.
147
148	Select:
149		--pid <pidlist>		Select by pid. This selects the blocks whose process ID
150					numbers appear in <pidlist>.
151		--tgid <tgidlist>	Select by tgid. This selects the blocks whose thread
152					group ID numbers appear in <tgidlist>.
153		--name <cmdlist>	Select by task command name. This selects the blocks whose
154					task command name appear in <cmdlist>.
155
156		<pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list,
157		which offers a way to specify individual selecting rules.
158
159
160		Examples:
161				./page_owner_sort <input> <output> --pid=1
162				./page_owner_sort <input> <output> --tgid=1,2,3
163				./page_owner_sort <input> <output> --name name1,name2
164
165STANDARD FORMAT SPECIFIERS
166==========================
167::
168
169  For --sort option:
170
171	KEY		LONG		DESCRIPTION
172	p		pid		process ID
173	tg		tgid		thread group ID
174	n		name		task command name
175	st		stacktrace	stack trace of the page allocation
176	T		txt		full text of block
177	ft		free_ts		timestamp of the page when it was released
178	at		alloc_ts	timestamp of the page when it was allocated
179	ator		allocator	memory allocator for pages
180
181  For --curl option:
182
183	KEY		LONG		DESCRIPTION
184	p		pid		process ID
185	tg		tgid		thread group ID
186	n		name		task command name
187	f		free		whether the page has been released or not
188	st		stacktrace	stack trace of the page allocation
189	ator		allocator	memory allocator for pages
190