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