1 ==================================================
2 page owner: Tracking about who allocated each page
3 ==================================================
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
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.
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.
27 page owner is disabled by default. So, if you'd like to use it, you need
28 to add "page_owner=on" to your boot cmdline. If the kernel is built
29 with page owner and page owner is disabled in runtime due to not enabling
30 boot option, runtime overhead is marginal. If disabled in runtime, it
31 doesn't require memory to store owner information, so there is no runtime
32 memory overhead. And, page owner inserts just two unlikely branches into
33 the page allocator hotpath and if not enabled, then allocation is done
34 like as the kernel without page owner. These two unlikely branches should
35 not affect to allocation performance, especially if the static keys jump
36 label patching functionality is available. Following is the kernel's code
37 size change due to this facility.
39 Although enabling page owner increases kernel size by several kilobytes,
40 most of this code is outside page allocator and its hot path. Building
41 the kernel with page owner and turning it on if needed would be great
42 option to debug kernel memory problem.
44 There is one notice that is caused by implementation detail. page owner
45 stores information into the memory from struct page extension. This memory
46 is initialized some time later than that page allocator starts in sparse
47 memory system, so, until initialization, many pages can be allocated and
48 they would have no owner information. To fix it up, these early allocated
49 pages are investigated and marked as allocated in initialization phase.
50 Although it doesn't mean that they have the right owner information,
51 at least, we can tell whether the page is allocated or not,
52 more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages
53 are caught and marked, although they are mostly allocated from struct
54 page extension feature. Anyway, after that, no page is left in
60 1) Build user-space helper::
65 2) Enable page owner: add "page_owner=on" to boot cmdline.
67 3) Do the job that you want to debug.
69 4) Analyze information from page owner::
71 cat /sys/kernel/debug/page_owner > page_owner_full.txt
72 ./page_owner_sort page_owner_full.txt sorted_page_owner.txt
74 The general output of ``page_owner_full.txt`` is as follows::
76 Page allocated via order XXX, ...
80 Page allocated via order XXX, ...
83 By default, it will do full pfn dump, to start with a given pfn,
84 page_owner supports fseek.
86 FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
87 fseek(fp, pfn_start, SEEK_SET);
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).
93 See the result about who allocated each page
94 in the ``sorted_page_owner.txt``. General output::
97 Page allocated via order XXX, ...
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:
104 fundamental function::
107 -a Sort by memory allocation time.
108 -m Sort by total memory.
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.
121 ./page_owner_sort <input> <output> --sort=n,+pid,-tgid
122 ./page_owner_sort <input> <output> --sort=at
124 additional function::
128 Specify culling rules.Culling syntax is key[,key[,...]].Choose a
129 multi-letter key from the **STANDARD FORMAT SPECIFIERS** section.
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.
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
144 -f Filter out the information of blocks whose memory has been released.
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>.
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.
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
163 STANDARD FORMAT SPECIFIERS
164 ==========================
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
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