Re: [PATCH v2 5/5] mm: add per-order mTHP swpin_refault counter

[Ryan Roberts]

On 09/04/2024 09:26, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
> 
> Currently, we are handling the scenario where we've hit a
> large folio in the swapcache, and the reclaiming process
> for this large folio is still ongoing.
> 
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
>  include/linux/huge_mm.h | 1 +
>  mm/huge_memory.c        | 2 ++
>  mm/memory.c             | 1 +
>  3 files changed, 4 insertions(+)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index c8256af83e33..b67294d5814f 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -269,6 +269,7 @@ enum mthp_stat_item {
>  	MTHP_STAT_ANON_ALLOC_FALLBACK,
>  	MTHP_STAT_ANON_SWPOUT,
>  	MTHP_STAT_ANON_SWPOUT_FALLBACK,
> +	MTHP_STAT_ANON_SWPIN_REFAULT,

I don't see any equivalent counter for small folios. Is there an analogue?

>  	__MTHP_STAT_COUNT
>  };
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d8d2ed80b0bf..fb95345b0bde 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -556,12 +556,14 @@ 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);
> +DEFINE_MTHP_STAT_ATTR(anon_swpin_refault, MTHP_STAT_ANON_SWPIN_REFAULT);
>  
>  static struct attribute *stats_attrs[] = {
>  	&anon_alloc_attr.attr,
>  	&anon_alloc_fallback_attr.attr,
>  	&anon_swpout_attr.attr,
>  	&anon_swpout_fallback_attr.attr,
> +	&anon_swpin_refault_attr.attr,
>  	NULL,
>  };
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 9818dc1893c8..acc023795a4d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4167,6 +4167,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  		nr_pages = nr;
>  		entry = folio->swap;
>  		page = &folio->page;
> +		count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_SWPIN_REFAULT);

I don't think this is the point of no return yet? There's the pte_same() check
immediately below (although I've suggested that needs to be moved to earlier),
but also the folio_test_uptodate() check. Perhaps this should go after that?

>  	}
>  
>  check_pte: