Re: [PATCH v2 1/2] mm: add per-order mTHP split counters

[Ryan Roberts <ryan.roberts@arm.com>]

On 28/06/2024 14:07, Lance Yang wrote:
> Currently, the split counters in THP statistics no longer include
> PTE-mapped mTHP. Therefore, we propose introducing per-order mTHP split
> counters to monitor the frequency of mTHP splits. This will help developers
> better analyze and optimize system performance.
> 
> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
>         split
>         split_failed
>         split_deferred
> 
> Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
> Signed-off-by: Lance Yang <ioworker0@gmail.com>

LGTM!

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

> ---
>  include/linux/huge_mm.h |  3 +++
>  mm/huge_memory.c        | 19 ++++++++++++++-----
>  2 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 212cca384d7e..cee3c5da8f0e 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -284,6 +284,9 @@ enum mthp_stat_item {
>  	MTHP_STAT_FILE_ALLOC,
>  	MTHP_STAT_FILE_FALLBACK,
>  	MTHP_STAT_FILE_FALLBACK_CHARGE,
> +	MTHP_STAT_SPLIT,
> +	MTHP_STAT_SPLIT_FAILED,
> +	MTHP_STAT_SPLIT_DEFERRED,
>  	__MTHP_STAT_COUNT
>  };
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c7ce28f6b7f3..a633206375af 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -559,6 +559,9 @@ DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
>  DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC);
>  DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK);
>  DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE);
> +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[] = {
>  	&anon_fault_alloc_attr.attr,
> @@ -569,6 +572,9 @@ static struct attribute *stats_attrs[] = {
>  	&file_alloc_attr.attr,
>  	&file_fallback_attr.attr,
>  	&file_fallback_charge_attr.attr,
> +	&split_attr.attr,
> +	&split_failed_attr.attr,
> +	&split_deferred_attr.attr,
>  	NULL,
>  };
>  
> @@ -3068,7 +3074,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  	XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);
>  	struct anon_vma *anon_vma = NULL;
>  	struct address_space *mapping = NULL;
> -	bool is_thp = folio_test_pmd_mappable(folio);
> +	int order = folio_order(folio);
>  	int extra_pins, ret;
>  	pgoff_t end;
>  	bool is_hzp;
> @@ -3076,7 +3082,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
>  	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>  
> -	if (new_order >= folio_order(folio))
> +	if (new_order >= order)
>  		return -EINVAL;
>  
>  	if (folio_test_anon(folio)) {
> @@ -3253,8 +3259,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
>  		i_mmap_unlock_read(mapping);
>  out:
>  	xas_destroy(&xas);
> -	if (is_thp)
> +	if (order >= HPAGE_PMD_ORDER)
>  		count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
> +	count_mthp_stat(order, !ret ? MTHP_STAT_SPLIT : MTHP_STAT_SPLIT_FAILED);
>  	return ret;
>  }
>  
> @@ -3278,13 +3285,14 @@ void deferred_split_folio(struct folio *folio)
>  #ifdef CONFIG_MEMCG
>  	struct mem_cgroup *memcg = folio_memcg(folio);
>  #endif
> +	int order = folio_order(folio);
>  	unsigned long flags;
>  
>  	/*
>  	 * Order 1 folios have no space for a deferred list, but we also
>  	 * won't waste much memory by not adding them to the deferred list.
>  	 */
> -	if (folio_order(folio) <= 1)
> +	if (order <= 1)
>  		return;
>  
>  	/*
> @@ -3305,8 +3313,9 @@ void deferred_split_folio(struct folio *folio)
>  
>  	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>  	if (list_empty(&folio->_deferred_list)) {
> -		if (folio_test_pmd_mappable(folio))
> +		if (order >= HPAGE_PMD_ORDER)
>  			count_vm_event(THP_DEFERRED_SPLIT_PAGE);
> +		count_mthp_stat(order, MTHP_STAT_SPLIT_DEFERRED);
>  		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
>  		ds_queue->split_queue_len++;
>  #ifdef CONFIG_MEMCG