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}[,compressed] 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 "compressed" optional parameter will try to store page tag references in a 28 compact format, avoiding page extensions. This results in improved performance 29 and memory consumption, however it might fail depending on system configuration. 30 If compression fails, a warning is issued and memory allocation profiling gets 31 disabled. 32 33sysctl: 34 /proc/sys/vm/mem_profiling 35 36 1: Enable memory profiling. 37 38 0: Disable memory profiling. 39 40 The default value depends on CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT. 41 42 When CONFIG_MEM_ALLOC_PROFILING_DEBUG=y, this control is read-only to avoid 43 warnings produced by allocations made while profiling is disabled and freed 44 when it's enabled. 45 46Runtime info: 47 /proc/allocinfo 48 49Example output:: 50 51 root@moria-kvm:~# sort -g /proc/allocinfo|tail|numfmt --to=iec 52 2.8M 22648 fs/kernfs/dir.c:615 func:__kernfs_new_node 53 3.8M 953 mm/memory.c:4214 func:alloc_anon_folio 54 4.0M 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start 55 4.1M 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable 56 6.0M 1532 mm/filemap.c:1919 func:__filemap_get_folio 57 8.8M 2785 kernel/fork.c:307 func:alloc_thread_stack_node 58 13M 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs 59 14M 3520 mm/mm_init.c:2530 func:alloc_large_system_hash 60 15M 3656 mm/readahead.c:247 func:page_cache_ra_unbounded 61 55M 4887 mm/slub.c:2259 func:alloc_slab_page 62 122M 31168 mm/page_ext.c:270 func:alloc_page_ext 63 64Theory of operation 65=================== 66 67Memory allocation profiling builds off of code tagging, which is a library for 68declaring static structs (that typically describe a file and line number in 69some way, hence code tagging) and then finding and operating on them at runtime, 70- i.e. iterating over them to print them in debugfs/procfs. 71 72To add accounting for an allocation call, we replace it with a macro 73invocation, alloc_hooks(), that 74- declares a code tag 75- stashes a pointer to it in task_struct 76- calls the real allocation function 77- and finally, restores the task_struct alloc tag pointer to its previous value. 78 79This allows for alloc_hooks() calls to be nested, with the most recent one 80taking effect. This is important for allocations internal to the mm/ code that 81do not properly belong to the outer allocation context and should be counted 82separately: for example, slab object extension vectors, or when the slab 83allocates pages from the page allocator. 84 85Thus, proper usage requires determining which function in an allocation call 86stack should be tagged. There are many helper functions that essentially wrap 87e.g. kmalloc() and do a little more work, then are called in multiple places; 88we'll generally want the accounting to happen in the callers of these helpers, 89not in the helpers themselves. 90 91To fix up a given helper, for example foo(), do the following: 92- switch its allocation call to the _noprof() version, e.g. kmalloc_noprof() 93 94- rename it to foo_noprof() 95 96- define a macro version of foo() like so: 97 98 #define foo(...) alloc_hooks(foo_noprof(__VA_ARGS__)) 99 100It's also possible to stash a pointer to an alloc tag in your own data structures. 101 102Do this when you're implementing a generic data structure that does allocations 103"on behalf of" some other code - for example, the rhashtable code. This way, 104instead of seeing a large line in /proc/allocinfo for rhashtable.c, we can 105break it out by rhashtable type. 106 107To do so: 108- Hook your data structure's init function, like any other allocation function. 109 110- Within your init function, use the convenience macro alloc_tag_record() to 111 record alloc tag in your data structure. 112 113- Then, use the following form for your allocations: 114 alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...)) 115