Re: [PATCH v3 2/2] mm: Tidy up shmem mTHP controls and stats

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/8/8 19:18, Ryan Roberts wrote:
> Previously we had a situation where shmem mTHP controls and stats were
> not exposed for some supported sizes and were exposed for some
> unsupported sizes. So let's clean that up.
> 
> Anon mTHP can support all large orders [2, PMD_ORDER]. But shmem can
> support all large orders [1, MAX_PAGECACHE_ORDER]. However, per-size
> shmem controls and stats were previously being exposed for all the anon
> mTHP orders, meaning order-1 was not present, and for arm64 64K base
> pages, orders 12 and 13 were exposed but were not supported internally.
> 
> Tidy this all up by defining ctrl and stats attribute groups for anon
> and file separately. Anon ctrl and stats groups are populated for all
> orders in THP_ORDERS_ALL_ANON and file ctrl and stats groups are
> populated for all orders in THP_ORDERS_ALL_FILE_DEFAULT.
> 
> Additionally, create "any" ctrl and stats attribute groups which are
> populated for all orders in (THP_ORDERS_ALL_ANON |
> THP_ORDERS_ALL_FILE_DEFAULT). swpout stats use this since they apply to
> anon and shmem.
> 
> The side-effect of all this is that different hugepage-*kB directories
> contain different sets of controls and stats, depending on which memory
> types support that size. This approach is preferred over the
> alternative, which is to populate dummy controls and stats for memory
> types that do not support a given size.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>   mm/huge_memory.c | 144 +++++++++++++++++++++++++++++++++++++----------
>   1 file changed, 114 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 0c3075ee00012..082d86b7c6c2f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -482,8 +482,8 @@ static void thpsize_release(struct kobject *kobj);
>   static DEFINE_SPINLOCK(huge_anon_orders_lock);
>   static LIST_HEAD(thpsize_list);
>   
> -static ssize_t thpsize_enabled_show(struct kobject *kobj,
> -				    struct kobj_attribute *attr, char *buf)
> +static ssize_t anon_enabled_show(struct kobject *kobj,
> +				 struct kobj_attribute *attr, char *buf)
>   {
>   	int order = to_thpsize(kobj)->order;
>   	const char *output;
> @@ -500,9 +500,9 @@ static ssize_t thpsize_enabled_show(struct kobject *kobj,
>   	return sysfs_emit(buf, "%s\n", output);
>   }
>   
> -static ssize_t thpsize_enabled_store(struct kobject *kobj,
> -				     struct kobj_attribute *attr,
> -				     const char *buf, size_t count)
> +static ssize_t anon_enabled_store(struct kobject *kobj,
> +				  struct kobj_attribute *attr,
> +				  const char *buf, size_t count)
>   {
>   	int order = to_thpsize(kobj)->order;
>   	ssize_t ret = count;
> @@ -544,19 +544,35 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
>   	return ret;
>   }
>   
> -static struct kobj_attribute thpsize_enabled_attr =
> -	__ATTR(enabled, 0644, thpsize_enabled_show, thpsize_enabled_store);
> +static struct kobj_attribute anon_enabled_attr =
> +	__ATTR(enabled, 0644, anon_enabled_show, anon_enabled_store);
>   
> -static struct attribute *thpsize_attrs[] = {
> -	&thpsize_enabled_attr.attr,
> +static struct attribute *anon_ctrl_attrs[] = {
> +	&anon_enabled_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group anon_ctrl_attr_grp = {
> +	.attrs = anon_ctrl_attrs,
> +};
> +
> +static struct attribute *file_ctrl_attrs[] = {
>   #ifdef CONFIG_SHMEM
>   	&thpsize_shmem_enabled_attr.attr,
>   #endif
>   	NULL,
>   };
>   
> -static const struct attribute_group thpsize_attr_group = {
> -	.attrs = thpsize_attrs,
> +static const struct attribute_group file_ctrl_attr_grp = {
> +	.attrs = file_ctrl_attrs,
> +};
> +
> +static struct attribute *any_ctrl_attrs[] = {
> +	NULL,
> +};
> +
> +static const struct attribute_group any_ctrl_attr_grp = {
> +	.attrs = any_ctrl_attrs,
>   };

I wonder why adding a NULL group?

>   
>   static const struct kobj_type thpsize_ktype = {
> @@ -595,64 +611,132 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
>   DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>   DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
>   DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
> +#ifdef CONFIG_SHMEM
>   DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC);
>   DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK);
>   DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE);
> +#endif
>   DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);
>   DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
>   DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
>   
> -static struct attribute *stats_attrs[] = {
> +static struct attribute *anon_stats_attrs[] = {
>   	&anon_fault_alloc_attr.attr,
>   	&anon_fault_fallback_attr.attr,
>   	&anon_fault_fallback_charge_attr.attr,
> +#ifndef CONFIG_SHMEM
>   	&swpout_attr.attr,
>   	&swpout_fallback_attr.attr,
> -	&shmem_alloc_attr.attr,
> -	&shmem_fallback_attr.attr,
> -	&shmem_fallback_charge_attr.attr,
> +#endif
>   	&split_attr.attr,
>   	&split_failed_attr.attr,
>   	&split_deferred_attr.attr,
>   	NULL,
>   };
>   
> -static struct attribute_group stats_attr_group = {
> +static struct attribute_group anon_stats_attr_grp = {
> +	.name = "stats",
> +	.attrs = anon_stats_attrs,
> +};
> +
> +static struct attribute *file_stats_attrs[] = {
> +#ifdef CONFIG_SHMEM
> +	&shmem_alloc_attr.attr,
> +	&shmem_fallback_attr.attr,
> +	&shmem_fallback_charge_attr.attr,
> +#endif
> +	NULL,
> +};
> +
> +static struct attribute_group file_stats_attr_grp = {
> +	.name = "stats",
> +	.attrs = file_stats_attrs,
> +};
> +
> +static struct attribute *any_stats_attrs[] = {
> +#ifdef CONFIG_SHMEM
> +	&swpout_attr.attr,
> +	&swpout_fallback_attr.attr,
> +#endif

Sorry I did not point it out in early version. I think file pages and 
shmem can also be split, while 'split_deferred' is only for anonymous 
page. So I think the any_stats_attrs should be:
static struct attribute *any_stats_attrs[] = {
#ifdef CONFIG_SHMEM
	&swpout_attr.attr,
	&swpout_fallback_attr.attr,
#endif
	&split_attr.attr,
	&split_failed_attr.attr,
	NULL,
};