On Thu, Mar 7, 2024 at 3:19 AM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: > > Hi, > This includes some editing suggestions and some doc build fixes. > > > On 3/6/24 10:24, Suren Baghdasaryan wrote: > > From: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > > > Provide documentation for memory allocation profiling. > > > > Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > --- > > 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 > > overhead is > > > + 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 > > typically > > > +some way, hence code tagging) and then finding and operating on them at runtime > > at runtime, > > > +- i.e. iterating over them to print them in debugfs/procfs. > > i.e., iterating > > > + > > +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 > > maybe end the line above with a '.' like the following line. > > > + - 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(...)) > > > Finally, there are a number of documentation build warnings in this patch. > I'm no ReST expert, but the attached patch fixes them for me. Thanks Randy! I'll use your cleaned-up patch in the next submission. Cheers, Suren. > > -- > #Randy
