Re: [PATCH] mm: slub: Convert sys slab alloc_calls, free_calls to bin attribute

[Vlastimil Babka]

On 1/12/21 10:21 AM, Faiyaz Mohammed wrote:
> Reading the sys slab alloc_calls, free_calls returns the available object
> owners, but the size of this file is limited to PAGE_SIZE
> because of the limitation of sysfs attributes, it is returning the
> partial owner info, which is not sufficient to debug/account the slab
> memory and alloc_calls output is not matching with /proc/slabinfo.
> 
> To remove the PAGE_SIZE limitation converted the sys slab
> alloc_calls, free_calls to bin attribute.
> 
> Signed-off-by: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx>
> ---
>  mm/slub.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 47 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index b52384e..8744e5ec 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4710,13 +4710,14 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s,
>  }
>  
>  static int list_locations(struct kmem_cache *s, char *buf,
> -					enum track_item alloc)
> +			loff_t offset, enum track_item alloc)
>  {
>  	int len = 0;
>  	unsigned long i;
>  	struct loc_track t = { 0, 0, NULL };
>  	int node;
>  	struct kmem_cache_node *n;
> +	static unsigned int previous_read_count;

Hmm static? What about parallel reads from different files? I guess you'll have
to somehow employ the offset parameter here and it won't be pretty, because you
are still printing free text and not some fixed-size binary chunks where seeking
is simple.
Also it's wasteful to to repeat the data gathering for each pritned page, you'd
need a mechanism that allows holding private data between printing out the
pages. If bin_attribute doesn't have that, you'd need e.g. seq_file which we use
for /proc/pid/(s)maps etc.

>  	unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);

This line doesn't exist since 90e9f6a66c78f in v5.6-rc1, is the patch based on
an old kernel?

>  	if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> @@ -4742,11 +4743,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
>  		spin_unlock_irqrestore(&n->list_lock, flags);
>  	}
>  
> -	for (i = 0; i < t.count; i++) {
> +	for (i = previous_read_count; i < t.count; i++) {
>  		struct location *l = &t.loc[i];
>  
> -		if (len > PAGE_SIZE - KSYM_SYMBOL_LEN - 100)
> -			break;
>  		len += sprintf(buf + len, "%7ld ", l->count);
>  
>  		if (l->addr)
> @@ -4784,12 +4783,20 @@ static int list_locations(struct kmem_cache *s, char *buf,
>  					 nodemask_pr_args(&l->nodes));
>  
>  		len += sprintf(buf + len, "\n");
> +
> +		if (len > PAGE_SIZE - KSYM_SYMBOL_LEN - 100) {
> +			previous_read_count = i + 1;
> +			break;
> +		}
>  	}
>  
> +	if ((offset != 0) && ((i >= t.count) || (previous_read_count > t.count))) {
> +		previous_read_count = 0;
> +		len = 0;
> +	} else if (!t.count)
> +		len += sprintf(buf, "No data\n");
>  	free_loc_track(&t);
>  	bitmap_free(map);
> -	if (!t.count)
> -		len += sprintf(buf, "No data\n");
>  	return len;
>  }
>  
> @@ -5180,6 +5187,7 @@ static int any_slab_objects(struct kmem_cache *s)
>  
>  struct slab_attribute {
>  	struct attribute attr;
> +	struct bin_attribute bin_attr;
>  	ssize_t (*show)(struct kmem_cache *s, char *buf);
>  	ssize_t (*store)(struct kmem_cache *s, const char *x, size_t count);
>  };
> @@ -5192,6 +5200,12 @@ struct slab_attribute {
>  	static struct slab_attribute _name##_attr =  \
>  	__ATTR(_name, 0600, _name##_show, _name##_store)
>  
> +#define SLAB_BIN_ATTR_RO(_name) \
> +	static struct slab_attribute _name##_attr = { \
> +	.bin_attr = \
> +	__BIN_ATTR_RO(_name, 0) \
> +	} \
> +
>  static ssize_t slab_size_show(struct kmem_cache *s, char *buf)
>  {
>  	return sprintf(buf, "%u\n", s->size);
> @@ -5535,21 +5549,33 @@ static ssize_t validate_store(struct kmem_cache *s,
>  }
>  SLAB_ATTR(validate);
>  
> -static ssize_t alloc_calls_show(struct kmem_cache *s, char *buf)
> +static ssize_t alloc_calls_read(struct file *filp, struct kobject *kobj,
> +				struct bin_attribute *bin_attr, char *buf,
> +					loff_t offset, size_t count)
>  {
> +	struct kmem_cache *s;
> +
> +	s = to_slab(kobj);
>  	if (!(s->flags & SLAB_STORE_USER))
>  		return -ENOSYS;
> -	return list_locations(s, buf, TRACK_ALLOC);
> +
> +	return list_locations(s, buf, offset, TRACK_ALLOC);
>  }
> -SLAB_ATTR_RO(alloc_calls);
> +SLAB_BIN_ATTR_RO(alloc_calls);
>  
> -static ssize_t free_calls_show(struct kmem_cache *s, char *buf)
> +static ssize_t free_calls_read(struct file *filp, struct kobject *kobj,
> +				struct bin_attribute *bin_attr, char *buf,
> +					loff_t offset, size_t count)
>  {
> +	struct kmem_cache *s;
> +
> +	s = to_slab(kobj);
>  	if (!(s->flags & SLAB_STORE_USER))
>  		return -ENOSYS;
> -	return list_locations(s, buf, TRACK_FREE);
> +
> +	return list_locations(s, buf, offset, TRACK_FREE);
>  }
> -SLAB_ATTR_RO(free_calls);
> +SLAB_BIN_ATTR_RO(free_calls);
>  #endif /* CONFIG_SLUB_DEBUG */
>  
>  #ifdef CONFIG_FAILSLAB
> @@ -5694,6 +5720,14 @@ STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node);
>  STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain);
>  #endif	/* CONFIG_SLUB_STATS */
>  
> +
> +static struct bin_attribute *slab_bin_attrs[] = {
> +#ifdef CONFIG_SLUB_DEBUG
> +	&alloc_calls_attr.bin_attr,
> +	&free_calls_attr.bin_attr,
> +#endif
> +};
> +
>  static struct attribute *slab_attrs[] = {
>  	&slab_size_attr.attr,
>  	&object_size_attr.attr,
> @@ -5722,8 +5756,6 @@ static struct attribute *slab_attrs[] = {
>  	&poison_attr.attr,
>  	&store_user_attr.attr,
>  	&validate_attr.attr,
> -	&alloc_calls_attr.attr,
> -	&free_calls_attr.attr,
>  #endif
>  #ifdef CONFIG_ZONE_DMA
>  	&cache_dma_attr.attr,
> @@ -5769,6 +5801,7 @@ static struct attribute *slab_attrs[] = {
>  
>  static const struct attribute_group slab_attr_group = {
>  	.attrs = slab_attrs,
> +	.bin_attrs = slab_bin_attrs,
>  };
>  
>  static ssize_t slab_attr_show(struct kobject *kobj,
>