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