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

[Vlastimil Babka <vbabka@suse.cz>]

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?

> 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 :)

> 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