Message-ID: <CAJuCfpFN3BLsFOWB0huA==LVa2pNYdnf7bT_VXgDtPuJOxvWSQ@mail.gmail.com>
Date: Thu, 7 Mar 2024 16:51:08 +0000
From: Suren Baghdasaryan <surenb@...gle.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: akpm@...ux-foundation.org, 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, jhubbard@...dia.com, 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, aliceryhl@...gle.com, 
	rientjes@...gle.com, minchan@...gle.com, kaleshsingh@...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: Re: [PATCH v5 37/37] memprofiling: Documentation

On Thu, Mar 7, 2024 at 3:19 AM Randy Dunlap <rdunlap@...radead.org> 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@...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 | 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@...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
>
>                                   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

Powered by blists - more mailing lists