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1What: /sys/kernel/debug/kmemtrace/
2Date: July 2008
3Contact: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
4Description:
5
6In kmemtrace-enabled kernels, the following files are created:
7
8/sys/kernel/debug/kmemtrace/
9 cpu<n> (0400) Per-CPU tracing data, see below. (binary)
10 total_overruns (0400) Total number of bytes which were dropped from
11 cpu<n> files because of full buffer condition,
12 non-binary. (text)
13 abi_version (0400) Kernel's kmemtrace ABI version. (text)
14
15Each per-CPU file should be read according to the relay interface. That is,
16the reader should set affinity to that specific CPU and, as currently done by
17the userspace application (though there are other methods), use poll() with
18an infinite timeout before every read(). Otherwise, erroneous data may be
19read. The binary data has the following _core_ format:
20
21 Event ID (1 byte) Unsigned integer, one of:
22 0 - represents an allocation (KMEMTRACE_EVENT_ALLOC)
23 1 - represents a freeing of previously allocated memory
24 (KMEMTRACE_EVENT_FREE)
25 Type ID (1 byte) Unsigned integer, one of:
26 0 - this is a kmalloc() / kfree()
27 1 - this is a kmem_cache_alloc() / kmem_cache_free()
28 2 - this is a __get_free_pages() et al.
29 Event size (2 bytes) Unsigned integer representing the
30 size of this event. Used to extend
31 kmemtrace. Discard the bytes you
32 don't know about.
33 Sequence number (4 bytes) Signed integer used to reorder data
34 logged on SMP machines. Wraparound
35 must be taken into account, although
36 it is unlikely.
37 Caller address (8 bytes) Return address to the caller.
38 Pointer to mem (8 bytes) Pointer to target memory area. Can be
39 NULL, but not all such calls might be
40 recorded.
41
42In case of KMEMTRACE_EVENT_ALLOC events, the next fields follow:
43
44 Requested bytes (8 bytes) Total number of requested bytes,
45 unsigned, must not be zero.
46 Allocated bytes (8 bytes) Total number of actually allocated
47 bytes, unsigned, must not be lower
48 than requested bytes.
49 Requested flags (4 bytes) GFP flags supplied by the caller.
50 Target CPU (4 bytes) Signed integer, valid for event id 1.
51 If equal to -1, target CPU is the same
52 as origin CPU, but the reverse might
53 not be true.
54
55The data is made available in the same endianness the machine has.
56
57Other event ids and type ids may be defined and added. Other fields may be
58added by increasing event size, but see below for details.
59Every modification to the ABI, including new id definitions, are followed
60by bumping the ABI version by one.
61
62Adding new data to the packet (features) is done at the end of the mandatory
63data:
64 Feature size (2 byte)
65 Feature ID (1 byte)
66 Feature data (Feature size - 3 bytes)
67
68
69Users:
70 kmemtrace-user - git://repo.or.cz/kmemtrace-user.git
71