Re: [PATCH v2 1/1] alloc_tag: mark inaccurate allocation counters in /proc/allocinfo output

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Sep 15, 2025 at 4:02 PM Suren Baghdasaryan <surenb@google.com> 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, "accurate:no" marker is appended to the call site
> line in the /proc/allocinfo output.
> Bump up /proc/allocinfo version to reflect the change in the file format
> and update documentation.
>
> 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 accurate:no
>            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 accurate:no
>        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>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Acked-by: Usama Arif <usamaarif642@gmail.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
> Changes since v1[1]:
> - Changed the marker from asterisk to accurate:no pair, per Andrew Morton
> - Documented /proc/allocinfo v2 format
> - Update the changelog
> - Added Acked-by from v2 since the functionality is the same,
> per Shakeel Butt, Usama Arif and Johannes Weiner


Sorry, forgot the --base=auto when formatting the patch. It's based on mm-new.

>
> [1] https://lore.kernel.org/all/20250909234942.1104356-1-surenb@google.com/
>
>  Documentation/filesystems/proc.rst |  4 ++++
>  include/linux/alloc_tag.h          | 12 ++++++++++++
>  include/linux/codetag.h            |  5 ++++-
>  lib/alloc_tag.c                    |  4 +++-
>  mm/slub.c                          |  2 ++
>  5 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 915a3e44bc12..1776a06571c2 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -1009,6 +1009,10 @@ number, module (if originates from a loadable module) and the function calling
>  the allocation. The number of bytes allocated and number of calls at each
>  location are reported. The first line indicates the version of the file, the
>  second line is the header listing fields in the file.
> +If file version is 2.0 or higher then each line may contain additional
> +<key>:<value> pairs representing extra information about the call site.
> +For example if the counters are not accurate, the line will be appended with
> +"accurate:no" pair.
>
>  Example output.
>
> 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 79891528e7b6..12ff80bbbd22 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");
>  }
>
> @@ -92,6 +92,8 @@ static void alloc_tag_to_text(struct seq_buf *out, struct codetag *ct)
>
>         seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls);
>         codetag_to_text(out, ct);
> +       if (unlikely(alloc_tag_is_inaccurate(tag)))
> +               seq_buf_printf(out, " accurate:no");
>         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
> --
> 2.51.0.384.g4c02a37b29-goog
>