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 in default. So, if you'd like to use it, you need 30to add "page_owner=on" into your boot cmdline. If the kernel is built 31with page owner and page owner is disabled in runtime due to no 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 what 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 See the result about who allocated each page 89 in the ``sorted_page_owner.txt``. 90