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 27It can also be used to show all the stacks and their outstanding 28allocations, which gives us a quick overview of where the memory is going 29without the need to screen through all the pages and match the allocation 30and free operation. 31 32page owner is disabled by default. So, if you'd like to use it, you need 33to add "page_owner=on" to your boot cmdline. If the kernel is built 34with page owner and page owner is disabled in runtime due to not enabling 35boot option, runtime overhead is marginal. If disabled in runtime, it 36doesn't require memory to store owner information, so there is no runtime 37memory overhead. And, page owner inserts just two unlikely branches into 38the page allocator hotpath and if not enabled, then allocation is done 39like as the kernel without page owner. These two unlikely branches should 40not affect to allocation performance, especially if the static keys jump 41label patching functionality is available. Following is the kernel's code 42size change due to this facility. 43 44Although enabling page owner increases kernel size by several kilobytes, 45most of this code is outside page allocator and its hot path. Building 46the kernel with page owner and turning it on if needed would be great 47option to debug kernel memory problem. 48 49There is one notice that is caused by implementation detail. page owner 50stores information into the memory from struct page extension. This memory 51is initialized some time later than that page allocator starts in sparse 52memory system, so, until initialization, many pages can be allocated and 53they would have no owner information. To fix it up, these early allocated 54pages are investigated and marked as allocated in initialization phase. 55Although it doesn't mean that they have the right owner information, 56at least, we can tell whether the page is allocated or not, 57more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages 58are caught and marked, although they are mostly allocated from struct 59page extension feature. Anyway, after that, no page is left in 60un-tracking state. 61 62Usage 63===== 64 651) Build user-space helper:: 66 67 cd tools/mm 68 make page_owner_sort 69 702) Enable page owner: add "page_owner=on" to boot cmdline. 71 723) Do the job that you want to debug. 73 744) Analyze information from page owner:: 75 76 cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt 77 cat stacks.txt 78 prep_new_page+0xa9/0x120 79 get_page_from_freelist+0x7e6/0x2140 80 __alloc_pages+0x18a/0x370 81 new_slab+0xc8/0x580 82 ___slab_alloc+0x1f2/0xaf0 83 __slab_alloc.isra.86+0x22/0x40 84 kmem_cache_alloc+0x31b/0x350 85 __khugepaged_enter+0x39/0x100 86 dup_mmap+0x1c7/0x5ce 87 copy_process+0x1afe/0x1c90 88 kernel_clone+0x9a/0x3c0 89 __do_sys_clone+0x66/0x90 90 do_syscall_64+0x7f/0x160 91 entry_SYSCALL_64_after_hwframe+0x6c/0x74 92 stack_count: 234 93 ... 94 ... 95 echo 7000 > /sys/kernel/debug/page_owner_stacks/count_threshold 96 cat /sys/kernel/debug/page_owner_stacks/show_stacks> stacks_7000.txt 97 cat stacks_7000.txt 98 prep_new_page+0xa9/0x120 99 get_page_from_freelist+0x7e6/0x2140 100 __alloc_pages+0x18a/0x370 101 alloc_pages_mpol+0xdf/0x1e0 102 folio_alloc+0x14/0x50 103 filemap_alloc_folio+0xb0/0x100 104 page_cache_ra_unbounded+0x97/0x180 105 filemap_fault+0x4b4/0x1200 106 __do_fault+0x2d/0x110 107 do_pte_missing+0x4b0/0xa30 108 __handle_mm_fault+0x7fa/0xb70 109 handle_mm_fault+0x125/0x300 110 do_user_addr_fault+0x3c9/0x840 111 exc_page_fault+0x68/0x150 112 asm_exc_page_fault+0x22/0x30 113 stack_count: 8248 114 ... 115 116 cat /sys/kernel/debug/page_owner > page_owner_full.txt 117 ./page_owner_sort page_owner_full.txt sorted_page_owner.txt 118 119 The general output of ``page_owner_full.txt`` is as follows:: 120 121 Page allocated via order XXX, ... 122 PFN XXX ... 123 // Detailed stack 124 125 Page allocated via order XXX, ... 126 PFN XXX ... 127 // Detailed stack 128 By default, it will do full pfn dump, to start with a given pfn, 129 page_owner supports fseek. 130 131 FILE *fp = fopen("/sys/kernel/debug/page_owner", "r"); 132 fseek(fp, pfn_start, SEEK_SET); 133 134 The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows 135 in buf, uses regexp to extract the page order value, counts the times 136 and pages of buf, and finally sorts them according to the parameter(s). 137 138 See the result about who allocated each page 139 in the ``sorted_page_owner.txt``. General output:: 140 141 XXX times, XXX pages: 142 Page allocated via order XXX, ... 143 // Detailed stack 144 145 By default, ``page_owner_sort`` is sorted according to the times of buf. 146 If you want to sort by the page nums of buf, use the ``-m`` parameter. 147 The detailed parameters are: 148 149 fundamental function:: 150 151 Sort: 152 -a Sort by memory allocation time. 153 -m Sort by total memory. 154 -p Sort by pid. 155 -P Sort by tgid. 156 -n Sort by task command name. 157 -r Sort by memory release time. 158 -s Sort by stack trace. 159 -t Sort by times (default). 160 --sort <order> Specify sorting order. Sorting syntax is [+|-]key[,[+|-]key[,...]]. 161 Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is 162 optional since default direction is increasing numerical or lexicographic 163 order. Mixed use of abbreviated and complete-form of keys is allowed. 164 165 Examples: 166 ./page_owner_sort <input> <output> --sort=n,+pid,-tgid 167 ./page_owner_sort <input> <output> --sort=at 168 169 additional function:: 170 171 Cull: 172 --cull <rules> 173 Specify culling rules.Culling syntax is key[,key[,...]].Choose a 174 multi-letter key from the **STANDARD FORMAT SPECIFIERS** section. 175 176 <rules> is a single argument in the form of a comma-separated list, 177 which offers a way to specify individual culling rules. The recognized 178 keywords are described in the **STANDARD FORMAT SPECIFIERS** section below. 179 <rules> can be specified by the sequence of keys k1,k2, ..., as described in 180 the STANDARD SORT KEYS section below. Mixed use of abbreviated and 181 complete-form of keys is allowed. 182 183 Examples: 184 ./page_owner_sort <input> <output> --cull=stacktrace 185 ./page_owner_sort <input> <output> --cull=st,pid,name 186 ./page_owner_sort <input> <output> --cull=n,f 187 188 Filter: 189 -f Filter out the information of blocks whose memory has been released. 190 191 Select: 192 --pid <pidlist> Select by pid. This selects the blocks whose process ID 193 numbers appear in <pidlist>. 194 --tgid <tgidlist> Select by tgid. This selects the blocks whose thread 195 group ID numbers appear in <tgidlist>. 196 --name <cmdlist> Select by task command name. This selects the blocks whose 197 task command name appear in <cmdlist>. 198 199 <pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list, 200 which offers a way to specify individual selecting rules. 201 202 203 Examples: 204 ./page_owner_sort <input> <output> --pid=1 205 ./page_owner_sort <input> <output> --tgid=1,2,3 206 ./page_owner_sort <input> <output> --name name1,name2 207 208STANDARD FORMAT SPECIFIERS 209========================== 210:: 211 212 For --sort option: 213 214 KEY LONG DESCRIPTION 215 p pid process ID 216 tg tgid thread group ID 217 n name task command name 218 st stacktrace stack trace of the page allocation 219 T txt full text of block 220 ft free_ts timestamp of the page when it was released 221 at alloc_ts timestamp of the page when it was allocated 222 ator allocator memory allocator for pages 223 224 For --cull option: 225 226 KEY LONG DESCRIPTION 227 p pid process ID 228 tg tgid thread group ID 229 n name task command name 230 f free whether the page has been released or not 231 st stacktrace stack trace of the page allocation 232 ator allocator memory allocator for pages 233