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/vm 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