83 lines
3.7 KiB
Plaintext
83 lines
3.7 KiB
Plaintext
|
page owner: Tracking about who allocated each page
|
||
|
|
-----------------------------------------------------------
|
||
|
|
|
||
|
|
* Introduction
|
||
|
|
|
||
|
|
page owner is for the tracking about who allocated each page.
|
||
|
|
It can be used to debug memory leak or to find a memory hogger.
|
||
|
|
When allocation happens, information about allocation such as call stack
|
||
|
|
and order of pages is stored into certain storage for each page.
|
||
|
|
When we need to know about status of all pages, we can get and analyze
|
||
|
|
this information.
|
||
|
|
|
||
|
|
Although we already have tracepoint for tracing page allocation/free,
|
||
|
|
using it for analyzing who allocate each page is rather complex. We need
|
||
|
|
to enlarge the trace buffer for preventing overlapping until userspace
|
||
|
|
program launched. And, launched program continually dump out the trace
|
||
|
|
buffer for later analysis and it would change system behviour with more
|
||
|
|
possibility rather than just keeping it in memory, so bad for debugging.
|
||
|
|
|
||
|
|
page owner can also be used for various purposes. For example, accurate
|
||
|
|
fragmentation statistics can be obtained through gfp flag information of
|
||
|
|
each page. It is already implemented and activated if page owner is
|
||
|
|
enabled. Other usages are more than welcome.
|
||
|
|
|
||
|
|
page owner is disabled in default. So, if you'd like to use it, you need
|
||
|
|
to add "page_owner=on" into your boot cmdline. If the kernel is built
|
||
|
|
with page owner and page owner is disabled in runtime due to no enabling
|
||
|
|
boot option, runtime overhead is marginal. If disabled in runtime, it
|
||
|
|
doesn't require memory to store owner information, so there is no runtime
|
||
|
|
memory overhead. And, page owner inserts just two unlikely branches into
|
||
|
|
the page allocator hotpath and if not enabled, then allocation is done
|
||
|
|
like as the kernel without page owner. These two unlikely branches should
|
||
|
|
not affect to allocation performance, especially if the static keys jump
|
||
|
|
label patching functionality is available. Following is the kernel's code
|
||
|
|
size change due to this facility.
|
||
|
|
|
||
|
|
- Without page owner
|
||
|
|
text data bss dec hex filename
|
||
|
|
40662 1493 644 42799 a72f mm/page_alloc.o
|
||
|
|
|
||
|
|
- With page owner
|
||
|
|
text data bss dec hex filename
|
||
|
|
40892 1493 644 43029 a815 mm/page_alloc.o
|
||
|
|
1427 24 8 1459 5b3 mm/page_ext.o
|
||
|
|
2722 50 0 2772 ad4 mm/page_owner.o
|
||
|
|
|
||
|
|
Although, roughly, 4 KB code is added in total, page_alloc.o increase by
|
||
|
|
230 bytes and only half of it is in hotpath. Building the kernel with
|
||
|
|
page owner and turning it on if needed would be great option to debug
|
||
|
|
kernel memory problem.
|
||
|
|
|
||
|
|
There is one notice that is caused by implementation detail. page owner
|
||
|
|
stores information into the memory from struct page extension. This memory
|
||
|
|
is initialized some time later than that page allocator starts in sparse
|
||
|
|
memory system, so, until initialization, many pages can be allocated and
|
||
|
|
they would have no owner information. To fix it up, these early allocated
|
||
|
|
pages are investigated and marked as allocated in initialization phase.
|
||
|
|
Although it doesn't mean that they have the right owner information,
|
||
|
|
at least, we can tell whether the page is allocated or not,
|
||
|
|
more accurately. On 2GB memory x86-64 VM box, 13343 early allocated pages
|
||
|
|
are catched and marked, although they are mostly allocated from struct
|
||
|
|
page extension feature. Anyway, after that, no page is left in
|
||
|
|
un-tracking state.
|
||
|
|
|
||
|
|
* Usage
|
||
|
|
|
||
|
|
1) Build user-space helper
|
||
|
|
cd tools/vm
|
||
|
|
make page_owner_sort
|
||
|
|
|
||
|
|
2) Enable page owner
|
||
|
|
Add "page_owner=on" to boot cmdline.
|
||
|
|
|
||
|
|
3) Do the job what you want to debug
|
||
|
|
|
||
|
|
4) Analyze information from page owner
|
||
|
|
cat /sys/kernel/debug/page_owner > page_owner_full.txt
|
||
|
|
grep -v ^PFN page_owner_full.txt > page_owner.txt
|
||
|
|
./page_owner_sort page_owner.txt sorted_page_owner.txt
|
||
|
|
|
||
|
|
See the result about who allocated each page
|
||
|
|
in the sorted_page_owner.txt.
|