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 49=================== 50Theory of operation 51=================== 52 53Memory allocation profiling builds off of code tagging, which is a library for 54declaring static structs (that typically describe a file and line number in 55some way, hence code tagging) and then finding and operating on them at runtime, 56- i.e. iterating over them to print them in debugfs/procfs. 57 58To add accounting for an allocation call, we replace it with a macro 59invocation, alloc_hooks(), that 60- declares a code tag 61- stashes a pointer to it in task_struct 62- calls the real allocation function 63- and finally, restores the task_struct alloc tag pointer to its previous value. 64 65This allows for alloc_hooks() calls to be nested, with the most recent one 66taking effect. This is important for allocations internal to the mm/ code that 67do not properly belong to the outer allocation context and should be counted 68separately: for example, slab object extension vectors, or when the slab 69allocates pages from the page allocator. 70 71Thus, proper usage requires determining which function in an allocation call 72stack should be tagged. There are many helper functions that essentially wrap 73e.g. kmalloc() and do a little more work, then are called in multiple places; 74we'll generally want the accounting to happen in the callers of these helpers, 75not in the helpers themselves. 76 77To fix up a given helper, for example foo(), do the following: 78- switch its allocation call to the _noprof() version, e.g. kmalloc_noprof() 79 80- rename it to foo_noprof() 81 82- define a macro version of foo() like so: 83 84 #define foo(...) alloc_hooks(foo_noprof(__VA_ARGS__)) 85 86It's also possible to stash a pointer to an alloc tag in your own data structures. 87 88Do this when you're implementing a generic data structure that does allocations 89"on behalf of" some other code - for example, the rhashtable code. This way, 90instead of seeing a large line in /proc/allocinfo for rhashtable.c, we can 91break it out by rhashtable type. 92 93To do so: 94- Hook your data structure's init function, like any other allocation function. 95 96- Within your init function, use the convenience macro alloc_tag_record() to 97 record alloc tag in your data structure. 98 99- Then, use the following form for your allocations: 100 alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...)) 101