Re: [PATCH v4 2/2] mm: add per-order mTHP anon_swpout and anon_swpout_fallback counters

[Ryan Roberts]

On 05/04/2024 11:27, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
> 
> This helps to display the fragmentation situation of the swapfile,
> knowing the proportion of how much we haven't split large folios.
> So far, we only support non-split swapout for anon memory, with
> the possibility of expanding to shmem in the future.  So, we add
> the "anon" prefix to the counter names.
> 
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
>  include/linux/huge_mm.h | 2 ++
>  mm/huge_memory.c        | 4 ++++
>  mm/page_io.c            | 6 +++++-
>  mm/vmscan.c             | 3 +++
>  4 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index c5d33017a4dd..1d893a358df6 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -267,6 +267,8 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>  enum mthp_stat_item {
>  	MTHP_STAT_ANON_ALLOC,
>  	MTHP_STAT_ANON_ALLOC_FALLBACK,
> +	MTHP_STAT_ANON_SWPOUT,
> +	MTHP_STAT_ANON_SWPOUT_FALLBACK,
>  	__MTHP_STAT_COUNT
>  };
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 5b875f0fc923..28113f8fdf18 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -554,10 +554,14 @@ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
>  
>  DEFINE_MTHP_STAT_ATTR(anon_alloc, MTHP_STAT_ANON_ALLOC);
>  DEFINE_MTHP_STAT_ATTR(anon_alloc_fallback, MTHP_STAT_ANON_ALLOC_FALLBACK);
> +DEFINE_MTHP_STAT_ATTR(anon_swpout, MTHP_STAT_ANON_SWPOUT);
> +DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, MTHP_STAT_ANON_SWPOUT_FALLBACK);
>  
>  static struct attribute *stats_attrs[] = {
>  	&anon_alloc_attr.attr,
>  	&anon_alloc_fallback_attr.attr,
> +	&anon_swpout_attr.attr,
> +	&anon_swpout_fallback_attr.attr,
>  	NULL,
>  };
>  
> diff --git a/mm/page_io.c b/mm/page_io.c
> index a9a7c236aecc..7669452e8b4d 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -212,13 +212,17 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
>  
>  static inline void count_swpout_vm_event(struct folio *folio)
>  {
> +	long nr_pages = folio_nr_pages(folio);
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  	if (unlikely(folio_test_pmd_mappable(folio))) {
>  		count_memcg_folio_events(folio, THP_SWPOUT, 1);
>  		count_vm_event(THP_SWPOUT);
>  	}
> +	if (nr_pages > 0)
> +		count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_SWPOUT);

I think you mean "nr_pages > 1"? Although as established in my comments against
patch 1, its safe to call for order-0, so could just unconditionally call this
(as you effectively are at the moment).

>  #endif
> -	count_vm_events(PSWPOUT, folio_nr_pages(folio));
> +	count_vm_events(PSWPOUT, nr_pages);
>  }
>  
>  #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ffc4553c8615..b30e6294f82a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1247,6 +1247,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>  						count_vm_event(
>  							THP_SWPOUT_FALLBACK);
>  					}
> +					if (nr_pages > 0)
> +						count_mthp_stat(get_order(nr_pages * PAGE_SIZE),
> +							MTHP_STAT_ANON_SWPOUT_FALLBACK);

Same comment.

>  #endif
>  					if (!add_to_swap(folio))
>  						goto activate_locked_split;