Re: [PATCH 1/1] mm: slub: Introduce one knob to control the track of slub object

[Kent Overstreet <kent.overstreet@linux.dev>]

On Wed, Jul 23, 2025 at 04:03:28PM +0800, Zhenhua Huang wrote:
> Mem profiling feature tracks both "alloc_slab_page"(page level) and slub
> object level allocations. To track object level allocations,
> slabobj_ext consumes 16 bytes per object for profiling slub object if
> CONFIG_MEMCG is set.
> Based on the data I've collected, this overhead accounts for approximately
> 5.7% of slub memory usage — a considerable cost.
> w/ noslub  slub_debug=-
> Slab:              87520 kB
> w/o noslub slub_debug=-
> Slab:              92812 kB
> 
> While In some scenarios, we may choose not to delve into SLUB allocation
> details if initial triage indicates that SLUB memory usage is within
> acceptable limits. To support this, a control knob is introduced to enable
> or disable SLUB object tracking.
> The "noslub" knob disables SLUB tracking, preventing further allocation of
> slabobj_ext structures.

...Have there been actual scenarios where this would be useful?

We've already got a knob for memory allocation profiling as a whole;
most allocations are slub allocations, so if you're looking at memory
allocation profiling you probably want slub.

> 
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>  Documentation/mm/allocation-profiling.rst |  7 +++++-
>  include/linux/alloc_tag.h                 |  8 +++++++
>  lib/alloc_tag.c                           | 26 +++++++++++++++++------
>  mm/slub.c                                 | 10 ++++-----
>  4 files changed, 38 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
> index 316311240e6a..9ecae74e0365 100644
> --- a/Documentation/mm/allocation-profiling.rst
> +++ b/Documentation/mm/allocation-profiling.rst
> @@ -18,7 +18,7 @@ kconfig options:
>    missing annotation
>  
>  Boot parameter:
> -  sysctl.vm.mem_profiling={0|1|never}[,compressed]
> +  sysctl.vm.mem_profiling={0|1|never}[,compressed][,noslub]
>  
>    When set to "never", memory allocation profiling overhead is minimized and it
>    cannot be enabled at runtime (sysctl becomes read-only).
> @@ -30,6 +30,11 @@ Boot parameter:
>    If compression fails, a warning is issued and memory allocation profiling gets
>    disabled.
>  
> +  The optional noslub parameter disables tracking of individual SLUB objects. This
> +  approach, similar to how page owner tracking works, relies on slub_debug for SLUB
> +  object insights instead. While this reduces memory overhead, it also limits the
> +  ability to observe detailed SLUB allocation behavior.
> +
>  sysctl:
>    /proc/sys/vm/mem_profiling
>  
> diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> index 8f7931eb7d16..af3c139712ce 100644
> --- a/include/linux/alloc_tag.h
> +++ b/include/linux/alloc_tag.h
> @@ -134,6 +134,13 @@ static inline bool mem_alloc_profiling_enabled(void)
>  				   &mem_alloc_profiling_key);
>  }
>  
> +DECLARE_STATIC_KEY_TRUE(slub_mem_alloc_profiling_key);
> +
> +static inline bool slub_mem_alloc_profiling_enabled(void)
> +{
> +	return static_key_enabled(&slub_mem_alloc_profiling_key);
> +}
> +
>  static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
>  {
>  	struct alloc_tag_counters v = { 0, 0 };
> @@ -227,6 +234,7 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
>  
>  #define DEFINE_ALLOC_TAG(_alloc_tag)
>  static inline bool mem_alloc_profiling_enabled(void) { return false; }
> +static inline bool slub_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) {}
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index 0142bc916f73..b79b0d987427 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -33,6 +33,8 @@ DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
>  EXPORT_SYMBOL(mem_alloc_profiling_key);
>  
>  DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
> +DEFINE_STATIC_KEY_TRUE(slub_mem_alloc_profiling_key);
> +EXPORT_SYMBOL(slub_mem_alloc_profiling_key);
>  
>  struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
>  unsigned long alloc_tag_ref_mask;
> @@ -710,6 +712,7 @@ static inline void free_mod_tags_mem(void) {}
>  static int __init setup_early_mem_profiling(char *str)
>  {
>  	bool compressed = false;
> +	bool noslub = false;
>  	bool enable;
>  
>  	if (!str || !str[0])
> @@ -725,16 +728,19 @@ static int __init setup_early_mem_profiling(char *str)
>  		if (kstrtobool(token, &enable))
>  			return -EINVAL;
>  
> -		if (str) {
> -
> -			if (strcmp(str, "compressed"))
> +		while ((token = strsep(&str, ",")) != NULL) {
> +			if (strcmp(token, "compressed") == 0)
> +				compressed = true;
> +			else if (strcmp(token, "noslub") == 0)
> +				noslub = true;
> +			else
>  				return -EINVAL;
> -
> -			compressed = true;
>  		}
>  		mem_profiling_support = true;
> -		pr_info("Memory allocation profiling is enabled %s compression and is turned %s!\n",
> -			compressed ? "with" : "without", enable ? "on" : "off");
> +		pr_info("Memory allocation profiling is enabled %s compression, %s slub track and is turned %s!\n",
> +			compressed ? "with" : "without",
> +			noslub ? "without" : "with",
> +			enable ? "on" : "off");
>  	}
>  
>  	if (enable != mem_alloc_profiling_enabled()) {
> @@ -749,6 +755,12 @@ static int __init setup_early_mem_profiling(char *str)
>  		else
>  			static_branch_disable(&mem_profiling_compressed);
>  	}
> +	if (noslub == static_key_enabled(&slub_mem_alloc_profiling_key)) {
> +		if (noslub)
> +			static_branch_disable(&slub_mem_alloc_profiling_key);
> +		else
> +			static_branch_enable(&slub_mem_alloc_profiling_key);
> +	}
>  
>  	return 0;
>  }
> diff --git a/mm/slub.c b/mm/slub.c
> index 31e11ef256f9..e8378b092b30 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2093,7 +2093,7 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
>  	return slab_obj_exts(slab) + obj_to_index(s, slab, p);
>  }
>  
> -/* Should be called only if mem_alloc_profiling_enabled() */
> +/* Should be called only if slub_mem_alloc_profiling_enabled() */
>  static noinline void
>  __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
>  {
> @@ -2102,7 +2102,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
>  	obj_exts = prepare_slab_obj_exts_hook(s, flags, object);
>  	/*
>  	 * Currently obj_exts is used only for allocation profiling.
> -	 * If other users appear then mem_alloc_profiling_enabled()
> +	 * If other users appear then slub_mem_alloc_profiling_enabled()
>  	 * check should be added before alloc_tag_add().
>  	 */
>  	if (likely(obj_exts))
> @@ -2112,11 +2112,11 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
>  static inline void
>  alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
>  {
> -	if (mem_alloc_profiling_enabled())
> +	if (slub_mem_alloc_profiling_enabled())
>  		__alloc_tagging_slab_alloc_hook(s, object, flags);
>  }
>  
> -/* Should be called only if mem_alloc_profiling_enabled() */
> +/* Should be called only if slub_mem_alloc_profiling_enabled() */
>  static noinline void
>  __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
>  			       int objects)
> @@ -2143,7 +2143,7 @@ static inline void
>  alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
>  			     int objects)
>  {
> -	if (mem_alloc_profiling_enabled())
> +	if (slub_mem_alloc_profiling_enabled())
>  		__alloc_tagging_slab_free_hook(s, slab, p, objects);
>  }
>  
> -- 
> 2.34.1
>