Date: Tue, 27 Feb 2024 08:10:43 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
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Subject: Re: [PATCH v4 00/36] Memory allocation profiling

On Tue, Feb 27, 2024 at 5:35 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 2/21/24 20:40, Suren Baghdasaryan wrote:
> > Overview:
> > Low overhead [1] per-callsite memory allocation profiling. Not just for
> > debug kernels, overhead low enough to be deployed in production.
> >
> > Example output:
> >   root@...ia-kvm:~# sort -rn /proc/allocinfo
> >    127664128    31168 mm/page_ext.c:270 func:alloc_page_ext
> >     56373248     4737 mm/slub.c:2259 func:alloc_slab_page
> >     14880768     3633 mm/readahead.c:247 func:page_cache_ra_unbounded
> >     14417920     3520 mm/mm_init.c:2530 func:alloc_large_system_hash
> >     13377536      234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
> >     11718656     2861 mm/filemap.c:1919 func:__filemap_get_folio
> >      9192960     2800 kernel/fork.c:307 func:alloc_thread_stack_node
> >      4206592        4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
> >      4136960     1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
> >      3940352      962 mm/memory.c:4214 func:alloc_anon_folio
> >      2894464    22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
> >      ...
> >
> > Since v3:
> >  - Dropped patch changing string_get_size() [2] as not needed
> >  - Dropped patch modifying xfs allocators [3] as non needed,
> >    per Dave Chinner
> >  - Added Reviewed-by, per Kees Cook
> >  - Moved prepare_slab_obj_exts_hook() and alloc_slab_obj_exts() where they
> >    are used, per Vlastimil Babka
> >  - Fixed SLAB_NO_OBJ_EXT definition to use unused bit, per Vlastimil Babka
> >  - Refactored patch [4] into other patches, per Vlastimil Babka
> >  - Replaced snprintf() with seq_buf_printf(), per Kees Cook
> >  - Changed output to report bytes, per Andrew Morton and Pasha Tatashin
> >  - Changed output to report [module] only for loadable modules,
> >    per Vlastimil Babka
> >  - Moved mem_alloc_profiling_enabled() check earlier, per Vlastimil Babka
> >  - Changed the code to handle page splitting to be more understandable,
> >    per Vlastimil Babka
> >  - Moved alloc_tagging_slab_free_hook(), mark_objexts_empty(),
> >    mark_failed_objexts_alloc() and handle_failed_objexts_alloc(),
> >    per Vlastimil Babka
> >  - Fixed loss of __alloc_size(1, 2) in kvmalloc functions,
> >    per Vlastimil Babka
> >  - Refactored the code in show_mem() to avoid memory allocations,
> >    per Michal Hocko
> >  - Changed to trylock in show_mem() to avoid blocking in atomic context,
> >    per Tetsuo Handa
> >  - Added mm mailing list into MAINTAINERS, per Kees Cook
> >  - Added base commit SHA, per Andy Shevchenko
> >  - Added a patch with documentation, per Jani Nikula
> >  - Fixed 0day bugs
> >  - Added benchmark results [5], per Steven Rostedt
> >  - Rebased over Linux 6.8-rc5
> >
> > Items not yet addressed:
> >  - An early_boot option to prevent pageext overhead. We are looking into
> >    ways for using the same sysctr instead of adding additional early boot
> >    parameter.
>
> I have reviewed the parts that integrate the tracking with page and slab
> allocators, and besides some details to improve it seems ok to me. The
> early boot option seems coming so that might eventually be suitable for
> build-time enablement in a distro kernel.

Thanks for reviewing Vlastimil!

>
> The macros (and their potential spread to upper layers to keep the
> information useful enough) are of course ugly, but guess it can't be
> currently helped and I'm unable to decide whether it's worth it or not.
> That's up to those providing their success stories I guess. If there's
> at least a path ahead to replace that part with compiler support in the
> future, great. So I'm not against merging this. BTW, do we know Linus's
> opinion on the macros approach?

We haven't run it by Linus specifically but hopefully we will see a
comment from him on the mailing list at some point.

>
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