Subject: Re: [PATCH v2 19/47] mm: thp: dynamically allocate the thp-related shrinkers

From: Muchun Song <[email-masked]>
Date: Wed, 26 Jul 2023 15:10:21 +0800

On 2023/7/24 17:43, Qi Zheng wrote:
> Use new APIs to dynamically allocate the thp-zero and thp-deferred_split
> shrinkers.
>
> Signed-off-by: Qi Zheng <[email-masked]>
> ---
>   mm/huge_memory.c | 69 +++++++++++++++++++++++++++++++-----------------
>   1 file changed, 45 insertions(+), 24 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8c94b34024a2..4db5a1834d81 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -65,7 +65,11 @@ unsigned long transparent_hugepage_flags __read_mostly =
>   	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
>   	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
>   
> -static struct shrinker deferred_split_shrinker;
> +static struct shrinker *deferred_split_shrinker;
> +static unsigned long deferred_split_count(struct shrinker *shrink,
> +					  struct shrink_control *sc);
> +static unsigned long deferred_split_scan(struct shrinker *shrink,
> +					 struct shrink_control *sc);
>   
>   static atomic_t huge_zero_refcount;
>   struct page *huge_zero_page __read_mostly;
> @@ -229,11 +233,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
>   	return 0;
>   }
>   
> -static struct shrinker huge_zero_page_shrinker = {
> -	.count_objects = shrink_huge_zero_page_count,
> -	.scan_objects = shrink_huge_zero_page_scan,
> -	.seeks = DEFAULT_SEEKS,
> -};
> +static struct shrinker *huge_zero_page_shrinker;

Same as patch #17.

>   
>   #ifdef CONFIG_SYSFS
>   static ssize_t enabled_show(struct kobject *kobj,
> @@ -454,6 +454,40 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
>   }
>   #endif /* CONFIG_SYSFS */
>   
> +static int thp_shrinker_init(void)

Better to declare it as __init.

> +{
> +	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
> +	if (!huge_zero_page_shrinker)
> +		return -ENOMEM;
> +
> +	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
> +						 SHRINKER_MEMCG_AWARE |
> +						 SHRINKER_NONSLAB,
> +						 "thp-deferred_split");
> +	if (!deferred_split_shrinker) {
> +		shrinker_free_non_registered(huge_zero_page_shrinker);
> +		return -ENOMEM;
> +	}
> +
> +	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
> +	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
> +	huge_zero_page_shrinker->seeks = DEFAULT_SEEKS;
> +	shrinker_register(huge_zero_page_shrinker);
> +
> +	deferred_split_shrinker->count_objects = deferred_split_count;
> +	deferred_split_shrinker->scan_objects = deferred_split_scan;
> +	deferred_split_shrinker->seeks = DEFAULT_SEEKS;
> +	shrinker_register(deferred_split_shrinker);
> +
> +	return 0;
> +}
> +
> +static void thp_shrinker_exit(void)

Same as here.

> +{
> +	shrinker_unregister(huge_zero_page_shrinker);
> +	shrinker_unregister(deferred_split_shrinker);
> +}
> +
>   static int __init hugepage_init(void)
>   {
>   	int err;
> @@ -482,12 +516,9 @@ static int __init hugepage_init(void)
>   	if (err)
>   		goto err_slab;
>   
> -	err = register_shrinker(&huge_zero_page_shrinker, "thp-zero");
> -	if (err)
> -		goto err_hzp_shrinker;
> -	err = register_shrinker(&deferred_split_shrinker, "thp-deferred_split");
> +	err = thp_shrinker_init();
>   	if (err)
> -		goto err_split_shrinker;
> +		goto err_shrinker;
>   
>   	/*
>   	 * By default disable transparent hugepages on smaller systems,
> @@ -505,10 +536,8 @@ static int __init hugepage_init(void)
>   
>   	return 0;
>   err_khugepaged:
> -	unregister_shrinker(&deferred_split_shrinker);
> -err_split_shrinker:
> -	unregister_shrinker(&huge_zero_page_shrinker);
> -err_hzp_shrinker:
> +	thp_shrinker_exit();
> +err_shrinker:
>   	khugepaged_destroy();
>   err_slab:
>   	hugepage_exit_sysfs(hugepage_kobj);
> @@ -2851,7 +2880,7 @@ void deferred_split_folio(struct folio *folio)
>   #ifdef CONFIG_MEMCG
>   		if (memcg)
>   			set_shrinker_bit(memcg, folio_nid(folio),
> -					 deferred_split_shrinker.id);
> +					 deferred_split_shrinker->id);
>   #endif
>   	}
>   	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> @@ -2925,14 +2954,6 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>   	return split;
>   }
>   
> -static struct shrinker deferred_split_shrinker = {
> -	.count_objects = deferred_split_count,
> -	.scan_objects = deferred_split_scan,
> -	.seeks = DEFAULT_SEEKS,
> -	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
> -		 SHRINKER_NONSLAB,
> -};
> -
>   #ifdef CONFIG_DEBUG_FS
>   static void split_huge_pages_all(void)
>   {