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Date: Wed, 21 Feb 2024 11:40:49 -0800 From: Suren Baghdasaryan <surenb@...gle.com> To: akpm@...ux-foundation.org Cc: kent.overstreet@...ux.dev, mhocko@...e.com, vbabka@...e.cz, hannes@...xchg.org, roman.gushchin@...ux.dev, mgorman@...e.de, dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com, penguin-kernel@...ove.sakura.ne.jp, corbet@....net, void@...ifault.com, peterz@...radead.org, juri.lelli@...hat.com, catalin.marinas@....com, will@...nel.org, arnd@...db.de, tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org, peterx@...hat.com, david@...hat.com, axboe@...nel.dk, mcgrof@...nel.org, masahiroy@...nel.org, nathan@...nel.org, dennis@...nel.org, tj@...nel.org, muchun.song@...ux.dev, rppt@...nel.org, paulmck@...nel.org, pasha.tatashin@...een.com, yosryahmed@...gle.com, yuzhao@...gle.com, dhowells@...hat.com, hughd@...gle.com, andreyknvl@...il.com, keescook@...omium.org, ndesaulniers@...gle.com, vvvvvv@...gle.com, gregkh@...uxfoundation.org, ebiggers@...gle.com, ytcoode@...il.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, bristot@...hat.com, vschneid@...hat.com, cl@...ux.com, penberg@...nel.org, iamjoonsoo.kim@....com, 42.hyeyoo@...il.com, glider@...gle.com, elver@...gle.com, dvyukov@...gle.com, shakeelb@...gle.com, songmuchun@...edance.com, jbaron@...mai.com, rientjes@...gle.com, minchan@...gle.com, kaleshsingh@...gle.com, surenb@...gle.com, kernel-team@...roid.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-modules@...r.kernel.org, kasan-dev@...glegroups.com, cgroups@...r.kernel.org Subject: [PATCH v4 36/36] memprofiling: Documentation From: Kent Overstreet <kent.overstreet@...ux.dev> Provide documentation for memory allocation profiling. Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com> --- Documentation/mm/allocation-profiling.rst | 86 +++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 Documentation/mm/allocation-profiling.rst diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst new file mode 100644 index 000000000000..2bcbd9e51fe4 --- /dev/null +++ b/Documentation/mm/allocation-profiling.rst @@ -0,0 +1,86 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========================== +MEMORY ALLOCATION PROFILING +=========================== + +Low overhead (suitable for production) accounting of all memory allocations, +tracked by file and line number. + +Usage: +kconfig options: + - CONFIG_MEM_ALLOC_PROFILING + - CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT + - CONFIG_MEM_ALLOC_PROFILING_DEBUG + adds warnings for allocations that weren't accounted because of a + missing annotation + +Boot parameter: + sysctl.vm.mem_profiling=1 + +sysctl: + /proc/sys/vm/mem_profiling + +Runtime info: + /proc/allocinfo + +Example output: + root@...ia-kvm:~# sort -g /proc/allocinfo|tail|numfmt --to=iec + 2.8M 22648 fs/kernfs/dir.c:615 func:__kernfs_new_node + 3.8M 953 mm/memory.c:4214 func:alloc_anon_folio + 4.0M 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start + 4.1M 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable + 6.0M 1532 mm/filemap.c:1919 func:__filemap_get_folio + 8.8M 2785 kernel/fork.c:307 func:alloc_thread_stack_node + 13M 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs + 14M 3520 mm/mm_init.c:2530 func:alloc_large_system_hash + 15M 3656 mm/readahead.c:247 func:page_cache_ra_unbounded + 55M 4887 mm/slub.c:2259 func:alloc_slab_page + 122M 31168 mm/page_ext.c:270 func:alloc_page_ext +=================== +Theory of operation +=================== + +Memory allocation profiling builds off of code tagging, which is a library for +declaring static structs (that typcially describe a file and line number in +some way, hence code tagging) and then finding and operating on them at runtime +- i.e. iterating over them to print them in debugfs/procfs. + +To add accounting for an allocation call, we replace it with a macro +invocation, alloc_hooks(), that + - declares a code tag + - stashes a pointer to it in task_struct + - calls the real allocation function + - and finally, restores the task_struct alloc tag pointer to its previous value. + +This allows for alloc_hooks() calls to be nested, with the most recent one +taking effect. This is important for allocations internal to the mm/ code that +do not properly belong to the outer allocation context and should be counted +separately: for example, slab object extension vectors, or when the slab +allocates pages from the page allocator. + +Thus, proper usage requires determining which function in an allocation call +stack should be tagged. There are many helper functions that essentially wrap +e.g. kmalloc() and do a little more work, then are called in multiple places; +we'll generally want the accounting to happen in the callers of these helpers, +not in the helpers themselves. + +To fix up a given helper, for example foo(), do the following: + - switch its allocation call to the _noprof() version, e.g. kmalloc_noprof() + - rename it to foo_noprof() + - define a macro version of foo() like so: + #define foo(...) alloc_hooks(foo_noprof(__VA_ARGS__)) + +It's also possible to stash a pointer to an alloc tag in your own data structures. + +Do this when you're implementing a generic data structure that does allocations +"on behalf of" some other code - for example, the rhashtable code. This way, +instead of seeing a large line in /proc/allocinfo for rhashtable.c, we can +break it out by rhashtable type. + +To do so: + - Hook your data structure's init function, like any other allocation function + - Within your init function, use the convenience macro alloc_tag_record() to + record alloc tag in your data structure. + - Then, use the following form for your allocations: + alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...)) -- 2.44.0.rc0.258.g7320e95886-goog
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