Re: [PATCH 1/1] alloc_tag: mark inaccurate allocation counters in /proc/allocinfo output

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Sep 9, 2025 at 11:25 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 9/10/25 01:49, Suren Baghdasaryan wrote:
> > While rare, memory allocation profiling can contain inaccurate counters
> > if slab object extension vector allocation fails. That allocation might
> > succeed later but prior to that, slab allocations that would have used
> > that object extension vector will not be accounted for. To indicate
> > incorrect counters, mark them with an asterisk in the /proc/allocinfo
> > output.
> > Bump up /proc/allocinfo version to reflect change in the file format.
>
> Since it's rare, is it worth the trouble?

Apparently they are seen in Meta's fleet which instigated this thread:
https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/

>
> > Example output with invalid counters:
> > allocinfo - version: 2.0
> >            0        0 arch/x86/kernel/kdebugfs.c:105 func:create_setup_data_nodes
> >            0        0 arch/x86/kernel/alternative.c:2090 func:alternatives_smp_module_add
> >           0*       0* arch/x86/kernel/alternative.c:127 func:__its_alloc
> >            0        0 arch/x86/kernel/fpu/regset.c:160 func:xstateregs_set
> >            0        0 arch/x86/kernel/fpu/xstate.c:1590 func:fpstate_realloc
> >            0        0 arch/x86/kernel/cpu/aperfmperf.c:379 func:arch_enable_hybrid_capacity_scale
> >            0        0 arch/x86/kernel/cpu/amd_cache_disable.c:258 func:init_amd_l3_attrs
> >       49152*      48* arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create
> >        32768        1 arch/x86/kernel/cpu/mce/genpool.c:132 func:mce_gen_pool_create
> >            0        0 arch/x86/kernel/cpu/mce/amd.c:1341 func:mce_threshold_create_device
> >
> > Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
>
> Here a link might have been helpful :)

Right, here it is and suggestion is in the last paragraph:
https://lore.kernel.org/all/20250519160846.GA773385@cmpxchg.org/

>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> > Patch is based on mm-new.
> >
> >  include/linux/alloc_tag.h | 12 ++++++++++++
> >  include/linux/codetag.h   |  5 ++++-
> >  lib/alloc_tag.c           |  7 +++++--
> >  mm/slub.c                 |  2 ++
> >  4 files changed, 23 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> > index 9ef2633e2c08..d40ac39bfbe8 100644
> > --- a/include/linux/alloc_tag.h
> > +++ b/include/linux/alloc_tag.h
> > @@ -221,6 +221,16 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
> >       ref->ct = NULL;
> >  }
> >
> > +static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
> > +{
> > +     tag->ct.flags |= CODETAG_FLAG_INACCURATE;
> > +}
> > +
> > +static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
> > +{
> > +     return !!(tag->ct.flags & CODETAG_FLAG_INACCURATE);
> > +}
> > +
> >  #define alloc_tag_record(p)  ((p) = current->alloc_tag)
> >
> >  #else /* CONFIG_MEM_ALLOC_PROFILING */
> > @@ -230,6 +240,8 @@ static inline bool mem_alloc_profiling_enabled(void) { return false; }
> >  static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,
> >                                size_t bytes) {}
> >  static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
> > +static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag) {}
> > +static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag) { return false; }
> >  #define alloc_tag_record(p)  do {} while (0)
> >
> >  #endif /* CONFIG_MEM_ALLOC_PROFILING */
> > diff --git a/include/linux/codetag.h b/include/linux/codetag.h
> > index 457ed8fd3214..8ea2a5f7c98a 100644
> > --- a/include/linux/codetag.h
> > +++ b/include/linux/codetag.h
> > @@ -16,13 +16,16 @@ struct module;
> >  #define CODETAG_SECTION_START_PREFIX "__start_"
> >  #define CODETAG_SECTION_STOP_PREFIX  "__stop_"
> >
> > +/* codetag flags */
> > +#define CODETAG_FLAG_INACCURATE      (1 << 0)
> > +
> >  /*
> >   * An instance of this structure is created in a special ELF section at every
> >   * code location being tagged.  At runtime, the special section is treated as
> >   * an array of these.
> >   */
> >  struct codetag {
> > -     unsigned int flags; /* used in later patches */
> > +     unsigned int flags;
> >       unsigned int lineno;
> >       const char *modname;
> >       const char *function;
> > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> > index e9b33848700a..a7f15117c759 100644
> > --- a/lib/alloc_tag.c
> > +++ b/lib/alloc_tag.c
> > @@ -80,7 +80,7 @@ static void allocinfo_stop(struct seq_file *m, void *arg)
> >  static void print_allocinfo_header(struct seq_buf *buf)
> >  {
> >       /* Output format version, so we can change it. */
> > -     seq_buf_printf(buf, "allocinfo - version: 1.0\n");
> > +     seq_buf_printf(buf, "allocinfo - version: 2.0\n");
> >       seq_buf_printf(buf, "#     <size>  <calls> <tag info>\n");
> >  }
> >
> > @@ -90,7 +90,10 @@ static void alloc_tag_to_text(struct seq_buf *out, struct codetag *ct)
> >       struct alloc_tag_counters counter = alloc_tag_read(tag);
> >       s64 bytes = counter.bytes;
> >
> > -     seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls);
> > +     if (unlikely(alloc_tag_is_inaccurate(tag)))
> > +             seq_buf_printf(out, "%11lli* %7llu* ", bytes, counter.calls);
> > +     else
> > +             seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls);
> >       codetag_to_text(out, ct);
> >       seq_buf_putc(out, ' ');
> >       seq_buf_putc(out, '\n');
> > diff --git a/mm/slub.c b/mm/slub.c
> > index af343ca570b5..9c04f29ee8de 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2143,6 +2143,8 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
> >        */
> >       if (likely(obj_exts))
> >               alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
> > +     else
> > +             alloc_tag_set_inaccurate(current->alloc_tag);
> >  }
> >
> >  static inline void
> >
> > base-commit: f4e8f46973fe0c0f579944a37e96ba9efbe00cca
>