Received-SPF: pass (google.com: domain of linux-kernel+bounces-94429-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Wed,  6 Mar 2024 10:24:35 -0800
In-Reply-To: <20240306182440.2003814-1-surenb@google.com>
Precedence: bulk
Mime-Version: 1.0
References: <20240306182440.2003814-1-surenb@google.com>
Message-ID: <20240306182440.2003814-38-surenb@google.com>
Subject: [PATCH v5 37/37] memprofiling: Documentation
From: Suren Baghdasaryan <surenb@google.com>
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
Content-Type: text/plain; charset="UTF-8"

From: Kent Overstreet <kent.overstreet@linux.dev>

Provide documentation for memory allocation profiling.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 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(...))
-- 
2.44.0.278.ge034bb2e1d-goog