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 41- Without page owner:: 42 43 text data bss dec hex filename 44 48392 2333 644 51369 c8a9 mm/page_alloc.o 45 46- With page owner:: 47 48 text data bss dec hex filename 49 48800 2445 644 51889 cab1 mm/page_alloc.o 50 6662 108 29 6799 1a8f mm/page_owner.o 51 1025 8 8 1041 411 mm/page_ext.o 52 53Although, roughly, 8 KB code is added in total, page_alloc.o increase by 54520 bytes and less than half of it is in hotpath. Building the kernel with 55page owner and turning it on if needed would be great option to debug 56kernel memory problem. 57 58There is one notice that is caused by implementation detail. page owner 59stores information into the memory from struct page extension. This memory 60is initialized some time later than that page allocator starts in sparse 61memory system, so, until initialization, many pages can be allocated and 62they would have no owner information. To fix it up, these early allocated 63pages are investigated and marked as allocated in initialization phase. 64Although it doesn't mean that they have the right owner information, 65at least, we can tell whether the page is allocated or not, 66more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages 67are catched and marked, although they are mostly allocated from struct 68page extension feature. Anyway, after that, no page is left in 69un-tracking state. 70 71Usage 72===== 73 741) Build user-space helper:: 75 76 cd tools/vm 77 make page_owner_sort 78 792) Enable page owner: add "page_owner=on" to boot cmdline. 80 813) Do the job that you want to debug. 82 834) Analyze information from page owner:: 84 85 cat /sys/kernel/debug/page_owner > page_owner_full.txt 86 ./page_owner_sort page_owner_full.txt sorted_page_owner.txt 87 88 The general output of ``page_owner_full.txt`` is as follows:: 89 90 Page allocated via order XXX, ... 91 PFN XXX ... 92 // Detailed stack 93 94 Page allocated via order XXX, ... 95 PFN XXX ... 96 // Detailed stack 97 98 The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows 99 in buf, uses regexp to extract the page order value, counts the times 100 and pages of buf, and finally sorts them according to the parameter(s). 101 102 See the result about who allocated each page 103 in the ``sorted_page_owner.txt``. General output:: 104 105 XXX times, XXX pages: 106 Page allocated via order XXX, ... 107 // Detailed stack 108 109 By default, ``page_owner_sort`` is sorted according to the times of buf. 110 If you want to sort by the page nums of buf, use the ``-m`` parameter. 111 The detailed parameters are: 112 113 fundamental function:: 114 115 Sort: 116 -a Sort by memory allocation time. 117 -m Sort by total memory. 118 -p Sort by pid. 119 -P Sort by tgid. 120 -n Sort by task command name. 121 -r Sort by memory release time. 122 -s Sort by stack trace. 123 -t Sort by times (default). 124 --sort <order> Specify sorting order. Sorting syntax is [+|-]key[,[+|-]key[,...]]. 125 Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is 126 optional since default direction is increasing numerical or lexicographic 127 order. Mixed use of abbreviated and complete-form of keys is allowed. 128 129 Examples: 130 ./page_owner_sort <input> <output> --sort=n,+pid,-tgid 131 ./page_owner_sort <input> <output> --sort=at 132 133 additional function:: 134 135 Cull: 136 --cull <rules> 137 Specify culling rules.Culling syntax is key[,key[,...]].Choose a 138 multi-letter key from the **STANDARD FORMAT SPECIFIERS** section. 139 140 <rules> is a single argument in the form of a comma-separated list, 141 which offers a way to specify individual culling rules. The recognized 142 keywords are described in the **STANDARD FORMAT SPECIFIERS** section below. 143 <rules> can be specified by the sequence of keys k1,k2, ..., as described in 144 the STANDARD SORT KEYS section below. Mixed use of abbreviated and 145 complete-form of keys is allowed. 146 147 Examples: 148 ./page_owner_sort <input> <output> --cull=stacktrace 149 ./page_owner_sort <input> <output> --cull=st,pid,name 150 ./page_owner_sort <input> <output> --cull=n,f 151 152 Filter: 153 -f Filter out the information of blocks whose memory has been released. 154 155 Select: 156 --pid <pidlist> Select by pid. This selects the blocks whose process ID 157 numbers appear in <pidlist>. 158 --tgid <tgidlist> Select by tgid. This selects the blocks whose thread 159 group ID numbers appear in <tgidlist>. 160 --name <cmdlist> Select by task command name. This selects the blocks whose 161 task command name appear in <cmdlist>. 162 163 <pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list, 164 which offers a way to specify individual selecting rules. 165 166 167 Examples: 168 ./page_owner_sort <input> <output> --pid=1 169 ./page_owner_sort <input> <output> --tgid=1,2,3 170 ./page_owner_sort <input> <output> --name name1,name2 171 172STANDARD FORMAT SPECIFIERS 173========================== 174:: 175 176 For --sort option: 177 178 KEY LONG DESCRIPTION 179 p pid process ID 180 tg tgid thread group ID 181 n name task command name 182 st stacktrace stack trace of the page allocation 183 T txt full text of block 184 ft free_ts timestamp of the page when it was released 185 at alloc_ts timestamp of the page when it was allocated 186 ator allocator memory allocator for pages 187 188 For --curl option: 189 190 KEY LONG DESCRIPTION 191 p pid process ID 192 tg tgid thread group ID 193 n name task command name 194 f free whether the page has been released or not 195 st stacktrace stack trace of the page allocation 196 ator allocator memory allocator for pages 197