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AJvYcCUNT3df4tbKHWtkSIOXV1urN02k7BgF6/2YwFOsoHTnkN+a3S9NOec0k1aE/8HAV2XP63kND5GnbE5a9vRBRK5PT1B6c0u5UMn/bdA9EQ== X-Gm-Message-State: AOJu0Yzu74d4HAsklT8bpoUdH3K3mFwCZut5PwPs8u5VifDVynBpOgw7 zypc/DSoy2xkzojHT+IY72ptxvXRq/iiGzjRWBggxgXHh1NxqR/CoVOe1oaq6nOMeIW8F8dP8OC /RA== X-Google-Smtp-Source: AGHT+IGSwvnidbX0/rOv0INS3he6frJgJB+IsYvN52GAPjMVdVuwPoKCHiyeHTzcN2rL9OOwKUgSVjL4/4I= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:85f0:e3db:db05:85e2]) (user=surenb job=sendgmr) by 2002:a25:2fc1:0:b0:dc6:ebd4:cca2 with SMTP id v184-20020a252fc1000000b00dc6ebd4cca2mr528159ybv.11.1709749563843; Wed, 06 Mar 2024 10:26:03 -0800 (PST) Date: Wed, 6 Mar 2024 10:24:35 -0800 In-Reply-To: <20240306182440.2003814-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-modules@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240306182440.2003814-1-surenb@google.com> X-Mailer: git-send-email 2.44.0.278.ge034bb2e1d-goog Message-ID: <20240306182440.2003814-38-surenb@google.com> Subject: [PATCH v5 37/37] memprofiling: Documentation From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: kent.overstreet@linux.dev, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, penguin-kernel@i-love.sakura.ne.jp, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, jhubbard@nvidia.com, tj@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, andreyknvl@gmail.com, keescook@chromium.org, ndesaulniers@google.com, vvvvvv@google.com, gregkh@linuxfoundation.org, ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.com, aliceryhl@google.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, surenb@google.com, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org From: Kent Overstreet Provide documentation for memory allocation profiling. Signed-off-by: Kent Overstreet Signed-off-by: Suren Baghdasaryan --- Documentation/mm/allocation-profiling.rst | 91 +++++++++++++++++++++++ 1 file changed, 91 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..8a862c7d3aab --- /dev/null +++ b/Documentation/mm/allocation-profiling.rst @@ -0,0 +1,91 @@ +.. 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=0|1|never + + When set to "never", memory allocation profiling overheads is minimized and it + cannot be enabled at runtime (sysctl becomes read-only). + When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y, default value is "1". + When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n, default value is "never". + +sysctl: + /proc/sys/vm/mem_profiling + +Runtime info: + /proc/allocinfo + +Example output: + root@moria-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(...))