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 current number of 28allocated base pages, which gives us a quick overview of where the memory 29is going without the need to screen through all the pages and match the 30allocation and free operation. It's also possible to show only a numeric 31identifier of all the stacks (without stack traces) and their number of 32allocated base pages (faster to read and parse, eg, for monitoring) that 33can be matched with stacks later (show_handles and show_stacks_handles). 34 35page owner is disabled by default. So, if you'd like to use it, you need 36to add "page_owner=on" to your boot cmdline. If the kernel is built 37with page owner and page owner is disabled in runtime due to not enabling 38boot option, runtime overhead is marginal. If disabled in runtime, it 39doesn't require memory to store owner information, so there is no runtime 40memory overhead. And, page owner inserts just two unlikely branches into 41the page allocator hotpath and if not enabled, then allocation is done 42like as the kernel without page owner. These two unlikely branches should 43not affect to allocation performance, especially if the static keys jump 44label patching functionality is available. Following is the kernel's code 45size change due to this facility. 46 47Although enabling page owner increases kernel size by several kilobytes, 48most of this code is outside page allocator and its hot path. Building 49the kernel with page owner and turning it on if needed would be great 50option to debug kernel memory problem. 51 52There is one notice that is caused by implementation detail. page owner 53stores information into the memory from struct page extension. This memory 54is initialized some time later than that page allocator starts in sparse 55memory system, so, until initialization, many pages can be allocated and 56they would have no owner information. To fix it up, these early allocated 57pages are investigated and marked as allocated in initialization phase. 58Although it doesn't mean that they have the right owner information, 59at least, we can tell whether the page is allocated or not, 60more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages 61are caught and marked, although they are mostly allocated from struct 62page extension feature. Anyway, after that, no page is left in 63un-tracking state. 64 65Usage 66===== 67 681) Build user-space helper:: 69 70 cd tools/mm 71 make page_owner_sort 72 732) Enable page owner: add "page_owner=on" to boot cmdline. 74 753) Do the job that you want to debug. 76 774) Analyze information from page owner:: 78 79 cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt 80 cat stacks.txt 81 post_alloc_hook+0x177/0x1a0 82 get_page_from_freelist+0xd01/0xd80 83 __alloc_pages+0x39e/0x7e0 84 allocate_slab+0xbc/0x3f0 85 ___slab_alloc+0x528/0x8a0 86 kmem_cache_alloc+0x224/0x3b0 87 sk_prot_alloc+0x58/0x1a0 88 sk_alloc+0x32/0x4f0 89 inet_create+0x427/0xb50 90 __sock_create+0x2e4/0x650 91 inet_ctl_sock_create+0x30/0x180 92 igmp_net_init+0xc1/0x130 93 ops_init+0x167/0x410 94 setup_net+0x304/0xa60 95 copy_net_ns+0x29b/0x4a0 96 create_new_namespaces+0x4a1/0x820 97 nr_base_pages: 16 98 ... 99 ... 100 echo 7000 > /sys/kernel/debug/page_owner_stacks/count_threshold 101 cat /sys/kernel/debug/page_owner_stacks/show_stacks> stacks_7000.txt 102 cat stacks_7000.txt 103 post_alloc_hook+0x177/0x1a0 104 get_page_from_freelist+0xd01/0xd80 105 __alloc_pages+0x39e/0x7e0 106 alloc_pages_mpol+0x22e/0x490 107 folio_alloc+0xd5/0x110 108 filemap_alloc_folio+0x78/0x230 109 page_cache_ra_order+0x287/0x6f0 110 filemap_get_pages+0x517/0x1160 111 filemap_read+0x304/0x9f0 112 xfs_file_buffered_read+0xe6/0x1d0 [xfs] 113 xfs_file_read_iter+0x1f0/0x380 [xfs] 114 __kernel_read+0x3b9/0x730 115 kernel_read_file+0x309/0x4d0 116 __do_sys_finit_module+0x381/0x730 117 do_syscall_64+0x8d/0x150 118 entry_SYSCALL_64_after_hwframe+0x62/0x6a 119 nr_base_pages: 20824 120 ... 121 122 cat /sys/kernel/debug/page_owner_stacks/show_handles > handles_7000.txt 123 cat handles_7000.txt 124 handle: 42 125 nr_base_pages: 20824 126 ... 127 128 cat /sys/kernel/debug/page_owner_stacks/show_stacks_handles > stacks_handles.txt 129 cat stacks_handles.txt 130 post_alloc_hook+0x177/0x1a0 131 get_page_from_freelist+0xd01/0xd80 132 __alloc_pages+0x39e/0x7e0 133 alloc_pages_mpol+0x22e/0x490 134 folio_alloc+0xd5/0x110 135 filemap_alloc_folio+0x78/0x230 136 page_cache_ra_order+0x287/0x6f0 137 filemap_get_pages+0x517/0x1160 138 filemap_read+0x304/0x9f0 139 xfs_file_buffered_read+0xe6/0x1d0 [xfs] 140 xfs_file_read_iter+0x1f0/0x380 [xfs] 141 __kernel_read+0x3b9/0x730 142 kernel_read_file+0x309/0x4d0 143 __do_sys_finit_module+0x381/0x730 144 do_syscall_64+0x8d/0x150 145 entry_SYSCALL_64_after_hwframe+0x62/0x6a 146 handle: 42 147 ... 148 149 cat /sys/kernel/debug/page_owner > page_owner_full.txt 150 ./page_owner_sort page_owner_full.txt sorted_page_owner.txt 151 152 The general output of ``page_owner_full.txt`` is as follows:: 153 154 Page allocated via order XXX, ... 155 PFN XXX ... 156 // Detailed stack 157 158 Page allocated via order XXX, ... 159 PFN XXX ... 160 // Detailed stack 161 By default, it will do full pfn dump, to start with a given pfn, 162 page_owner supports fseek. 163 164 FILE *fp = fopen("/sys/kernel/debug/page_owner", "r"); 165 fseek(fp, pfn_start, SEEK_SET); 166 167 The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows 168 in buf, uses regexp to extract the page order value, counts the times 169 and pages of buf, and finally sorts them according to the parameter(s). 170 171 See the result about who allocated each page 172 in the ``sorted_page_owner.txt``. General output:: 173 174 XXX times, XXX pages: 175 Page allocated via order XXX, ... 176 // Detailed stack 177 178 By default, ``page_owner_sort`` is sorted according to the times of buf. 179 If you want to sort by the page nums of buf, use the ``-m`` parameter. 180 The detailed parameters are: 181 182 fundamental function:: 183 184 Sort: 185 -a Sort by memory allocation time. 186 -m Sort by total memory. 187 -p Sort by pid. 188 -P Sort by tgid. 189 -n Sort by task command name. 190 -r Sort by memory release time. 191 -s Sort by stack trace. 192 -t Sort by times (default). 193 --sort <order> Specify sorting order. Sorting syntax is [+|-]key[,[+|-]key[,...]]. 194 Choose a key from the **STANDARD FORMAT SPECIFIERS** section. The "+" is 195 optional since default direction is increasing numerical or lexicographic 196 order. Mixed use of abbreviated and complete-form of keys is allowed. 197 198 Examples: 199 ./page_owner_sort <input> <output> --sort=n,+pid,-tgid 200 ./page_owner_sort <input> <output> --sort=at 201 202 additional function:: 203 204 Cull: 205 --cull <rules> 206 Specify culling rules.Culling syntax is key[,key[,...]].Choose a 207 multi-letter key from the **STANDARD FORMAT SPECIFIERS** section. 208 209 <rules> is a single argument in the form of a comma-separated list, 210 which offers a way to specify individual culling rules. The recognized 211 keywords are described in the **STANDARD FORMAT SPECIFIERS** section below. 212 <rules> can be specified by the sequence of keys k1,k2, ..., as described in 213 the STANDARD SORT KEYS section below. Mixed use of abbreviated and 214 complete-form of keys is allowed. 215 216 Examples: 217 ./page_owner_sort <input> <output> --cull=stacktrace 218 ./page_owner_sort <input> <output> --cull=st,pid,name 219 ./page_owner_sort <input> <output> --cull=n,f 220 221 Filter: 222 -f Filter out the information of blocks whose memory has been released. 223 224 Select: 225 --pid <pidlist> Select by pid. This selects the blocks whose process ID 226 numbers appear in <pidlist>. 227 --tgid <tgidlist> Select by tgid. This selects the blocks whose thread 228 group ID numbers appear in <tgidlist>. 229 --name <cmdlist> Select by task command name. This selects the blocks whose 230 task command name appear in <cmdlist>. 231 232 <pidlist>, <tgidlist>, <cmdlist> are single arguments in the form of a comma-separated list, 233 which offers a way to specify individual selecting rules. 234 235 236 Examples: 237 ./page_owner_sort <input> <output> --pid=1 238 ./page_owner_sort <input> <output> --tgid=1,2,3 239 ./page_owner_sort <input> <output> --name name1,name2 240 241STANDARD FORMAT SPECIFIERS 242========================== 243:: 244 245 For --sort option: 246 247 KEY LONG DESCRIPTION 248 p pid process ID 249 tg tgid thread group ID 250 n name task command name 251 st stacktrace stack trace of the page allocation 252 T txt full text of block 253 ft free_ts timestamp of the page when it was released 254 at alloc_ts timestamp of the page when it was allocated 255 ator allocator memory allocator for pages 256 257 For --cull option: 258 259 KEY LONG DESCRIPTION 260 p pid process ID 261 tg tgid thread group ID 262 n name task command name 263 f free whether the page has been released or not 264 st stacktrace stack trace of the page allocation 265 ator allocator memory allocator for pages 266