1.. SPDX-License-Identifier: GPL-2.0
2
3===========================
4MEMORY ALLOCATION PROFILING
5===========================
6
7Low overhead (suitable for production) accounting of all memory allocations,
8tracked by file and line number.
9
10Usage:
11kconfig options:
12- CONFIG_MEM_ALLOC_PROFILING
13
14- CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
15
16- CONFIG_MEM_ALLOC_PROFILING_DEBUG
17  adds warnings for allocations that weren't accounted because of a
18  missing annotation
19
20Boot parameter:
21  sysctl.vm.mem_profiling=0|1|never
22
23  When set to "never", memory allocation profiling overhead is minimized and it
24  cannot be enabled at runtime (sysctl becomes read-only).
25  When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y, default value is "1".
26  When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n, default value is "never".
27
28sysctl:
29  /proc/sys/vm/mem_profiling
30
31Runtime info:
32  /proc/allocinfo
33
34Example output::
35
36  root@moria-kvm:~# sort -g /proc/allocinfo|tail|numfmt --to=iec
37        2.8M    22648 fs/kernfs/dir.c:615 func:__kernfs_new_node
38        3.8M      953 mm/memory.c:4214 func:alloc_anon_folio
39        4.0M     1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
40        4.1M        4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
41        6.0M     1532 mm/filemap.c:1919 func:__filemap_get_folio
42        8.8M     2785 kernel/fork.c:307 func:alloc_thread_stack_node
43         13M      234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
44         14M     3520 mm/mm_init.c:2530 func:alloc_large_system_hash
45         15M     3656 mm/readahead.c:247 func:page_cache_ra_unbounded
46         55M     4887 mm/slub.c:2259 func:alloc_slab_page
47        122M    31168 mm/page_ext.c:270 func:alloc_page_ext
48
49Theory of operation
50===================
51
52Memory allocation profiling builds off of code tagging, which is a library for
53declaring static structs (that typically describe a file and line number in
54some way, hence code tagging) and then finding and operating on them at runtime,
55- i.e. iterating over them to print them in debugfs/procfs.
56
57To add accounting for an allocation call, we replace it with a macro
58invocation, alloc_hooks(), that
59- declares a code tag
60- stashes a pointer to it in task_struct
61- calls the real allocation function
62- and finally, restores the task_struct alloc tag pointer to its previous value.
63
64This allows for alloc_hooks() calls to be nested, with the most recent one
65taking effect. This is important for allocations internal to the mm/ code that
66do not properly belong to the outer allocation context and should be counted
67separately: for example, slab object extension vectors, or when the slab
68allocates pages from the page allocator.
69
70Thus, proper usage requires determining which function in an allocation call
71stack should be tagged. There are many helper functions that essentially wrap
72e.g. kmalloc() and do a little more work, then are called in multiple places;
73we'll generally want the accounting to happen in the callers of these helpers,
74not in the helpers themselves.
75
76To fix up a given helper, for example foo(), do the following:
77- switch its allocation call to the _noprof() version, e.g. kmalloc_noprof()
78
79- rename it to foo_noprof()
80
81- define a macro version of foo() like so:
82
83  #define foo(...) alloc_hooks(foo_noprof(__VA_ARGS__))
84
85It's also possible to stash a pointer to an alloc tag in your own data structures.
86
87Do this when you're implementing a generic data structure that does allocations
88"on behalf of" some other code - for example, the rhashtable code. This way,
89instead of seeing a large line in /proc/allocinfo for rhashtable.c, we can
90break it out by rhashtable type.
91
92To do so:
93- Hook your data structure's init function, like any other allocation function.
94
95- Within your init function, use the convenience macro alloc_tag_record() to
96  record alloc tag in your data structure.
97
98- Then, use the following form for your allocations:
99  alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...))
100