1 ==================================================
2 page owner: Tracking about who allocated each page
3 ==================================================
4
5 Introduction
6 ============
7
8 page owner is for the tracking about who allocated each page.
9 It can be used to debug memory leak or to find a memory hogger.
10 When allocation happens, information about allocation such as call stack
11 and order of pages is stored into certain storage for each page.
12 When we need to know about status of all pages, we can get and analyze
13 this information.
14
15 Although we already have tracepoint for tracing page allocation/free,
16 using it for analyzing who allocate each page is rather complex. We need
17 to enlarge the trace buffer for preventing overlapping until userspace
18 program launched. And, launched program continually dump out the trace
19 buffer for later analysis and it would change system behaviour with more
20 possibility rather than just keeping it in memory, so bad for debugging.
21
22 page owner can also be used for various purposes. For example, accurate
23 fragmentation statistics can be obtained through gfp flag information of
24 each page. It is already implemented and activated if page owner is
25 enabled. Other usages are more than welcome.
26
27 It can also be used to show all the stacks and their current number of
28 allocated base pages, which gives us a quick overview of where the memory
29 is going without the need to screen through all the pages and match the
30 allocation and free operation.
31
32 page owner is disabled by default. So, if you'd like to use it, you need
33 to add "page_owner=on" to your boot cmdline. If the kernel is built
34 with page owner and page owner is disabled in runtime due to not enabling
35 boot option, runtime overhead is marginal. If disabled in runtime, it
36 doesn't require memory to store owner information, so there is no runtime
37 memory overhead. And, page owner inserts just two unlikely branches into
38 the page allocator hotpath and if not enabled, then allocation is done
39 like as the kernel without page owner. These two unlikely branches should
40 not affect to allocation performance, especially if the static keys jump
41 label patching functionality is available. Following is the kernel's code
42 size change due to this facility.
43
44 Although enabling page owner increases kernel size by several kilobytes,
45 most of this code is outside page allocator and its hot path. Building
46 the kernel with page owner and turning it on if needed would be great
47 option to debug kernel memory problem.
48
49 There is one notice that is caused by implementation detail. page owner
50 stores information into the memory from struct page extension. This memory
51 is initialized some time later than that page allocator starts in sparse
52 memory system, so, until initialization, many pages can be allocated and
53 they would have no owner information. To fix it up, these early allocated
54 pages are investigated and marked as allocated in initialization phase.
55 Although it doesn't mean that they have the right owner information,
56 at least, we can tell whether the page is allocated or not,
57 more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages
58 are caught and marked, although they are mostly allocated from struct
59 page extension feature. Anyway, after that, no page is left in
60 un-tracking state.
61
62 Usage
63 =====
64
65 1) Build user-space helper::
66
67 cd tools/mm
68 make page_owner_sort
69
70 2) Enable page owner: add "page_owner=on" to boot cmdline.
71
72 3) Do the job that you want to debug.
73
74 4) Analyze information from page owner::
75
76 cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt
77 cat stacks.txt
78 post_alloc_hook+0x177/0x1a0
79 get_page_from_freelist+0xd01/0xd80
80 __alloc_pages+0x39e/0x7e0
81 allocate_slab+0xbc/0x3f0
82 ___slab_alloc+0x528/0x8a0
83 kmem_cache_alloc+0x224/0x3b0
84 sk_prot_alloc+0x58/0x1a0
85 sk_alloc+0x32/0x4f0
86 inet_create+0x427/0xb50
87 __sock_create+0x2e4/0x650
88 inet_ctl_sock_create+0x30/0x180
89 igmp_net_init+0xc1/0x130
90 ops_init+0x167/0x410
91 setup_net+0x304/0xa60
92 copy_net_ns+0x29b/0x4a0
93 create_new_namespaces+0x4a1/0x820
94 nr_base_pages: 16
95 ...
96 ...
97 echo 7000 > /sys/kernel/debug/page_owner_stacks/count_threshold
98 cat /sys/kernel/debug/page_owner_stacks/show_stacks> stacks_7000.txt
99 cat stacks_7000.txt
100 post_alloc_hook+0x177/0x1a0
101 get_page_from_freelist+0xd01/0xd80
102 __alloc_pages+0x39e/0x7e0
103 alloc_pages_mpol+0x22e/0x490
104 folio_alloc+0xd5/0x110
105 filemap_alloc_folio+0x78/0x230
106 page_cache_ra_order+0x287/0x6f0
107 filemap_get_pages+0x517/0x1160
108 filemap_read+0x304/0x9f0
109 xfs_file_buffered_read+0xe6/0x1d0 [xfs]
110 xfs_file_read_iter+0x1f0/0x380 [xfs]
111 __kernel_read+0x3b9/0x730
112 kernel_read_file+0x309/0x4d0
113 __do_sys_finit_module+0x381/0x730
114 do_syscall_64+0x8d/0x150
115 entry_SYSCALL_64_after_hwframe+0x62/0x6a
116 nr_base_pages: 20824
117 ...
118
119 cat /sys/kernel/debug/page_owner > page_owner_full.txt
120 ./page_owner_sort page_owner_full.txt sorted_page_owner.txt
121
122 The general output of ``page_owner_full.txt`` is as follows::
123
124 Page allocated via order XXX, ...
125 PFN XXX ...
126 // Detailed stack
127
128 Page allocated via order XXX, ...
129 PFN XXX ...
130 // Detailed stack
131 By default, it will do full pfn dump, to start with a given pfn,
132 page_owner supports fseek.
133
134 FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
135 fseek(fp, pfn_start, SEEK_SET);
136
137 The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows
138 in buf, uses regexp to extract the page order value, counts the times
139 and pages of buf, and finally sorts them according to the parameter(s).
140
141 See the result about who allocated each page
142 in the ``sorted_page_owner.txt``. General output::
143
144 XXX times, XXX pages:
145 Page allocated via order XXX, ...
146 // Detailed stack
147
148 By default, ``page_owner_sort`` is sorted according to the times of buf.
149 If you want to sort by the page nums of buf, use the ``-m`` parameter.
150 The detailed parameters are:
151
152 fundamental function::
153
154 Sort:
155 -a Sort by memory allocation time.
156 -m Sort by total memory.
157 -p Sort by pid.
158 -P Sort by tgid.
159 -n Sort by task command name.
160 -r Sort by memory release time.
161 -s Sort by stack trace.
162 -t Sort by times (default).
163 --sort <order> Specify sorting order. Sorting syntax is [+|-]key[,[+|-]key[,...]].
164 Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is
165 optional since default direction is increasing numerical or lexicographic
166 order. Mixed use of abbreviated and complete-form of keys is allowed.
167
168 Examples:
169 ./page_owner_sort <input> <output> --sort=n,+pid,-tgid
170 ./page_owner_sort <input> <output> --sort=at
171
172 additional function::
173
174 Cull:
175 --cull <rules>
176 Specify culling rules.Culling syntax is key[,key[,...]].Choose a
177 multi-letter key from the **STANDARD FORMAT SPECIFIERS** section.
178
179 <rules> is a single argument in the form of a comma-separated list,
180 which offers a way to specify individual culling rules. The recognized
181 keywords are described in the **STANDARD FORMAT SPECIFIERS** section below.
182 <rules> can be specified by the sequence of keys k1,k2, ..., as described in
183 the STANDARD SORT KEYS section below. Mixed use of abbreviated and
184 complete-form of keys is allowed.
185
186 Examples:
187 ./page_owner_sort <input> <output> --cull=stacktrace
188 ./page_owner_sort <input> <output> --cull=st,pid,name
189 ./page_owner_sort <input> <output> --cull=n,f
190
191 Filter:
192 -f Filter out the information of blocks whose memory has been released.
193
194 Select:
195 --pid <pidlist> Select by pid. This selects the blocks whose process ID
196 numbers appear in <pidlist>.
197 --tgid <tgidlist> Select by tgid. This selects the blocks whose thread
198 group ID numbers appear in <tgidlist>.
199 --name <cmdlist> Select by task command name. This selects the blocks whose
200 task command name appear in <cmdlist>.
201
202 <pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list,
203 which offers a way to specify individual selecting rules.
204
205
206 Examples:
207 ./page_owner_sort <input> <output> --pid=1
208 ./page_owner_sort <input> <output> --tgid=1,2,3
209 ./page_owner_sort <input> <output> --name name1,name2
210
211 STANDARD FORMAT SPECIFIERS
212 ==========================
213 ::
214
215 For --sort option:
216
217 KEY LONG DESCRIPTION
218 p pid process ID
219 tg tgid thread group ID
220 n name task command name
221 st stacktrace stack trace of the page allocation
222 T txt full text of block
223 ft free_ts timestamp of the page when it was released
224 at alloc_ts timestamp of the page when it was allocated
225 ator allocator memory allocator for pages
226
227 For --cull option:
228
229 KEY LONG DESCRIPTION
230 p pid process ID
231 tg tgid thread group ID
232 n name task command name
233 f free whether the page has been released or not
234 st stacktrace stack trace of the page allocation
235 ator allocator memory allocator for pages
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