Re: [PATCH v3] mm: add per-order mTHP swap-in fallback/fallback_charge counters

[Lance Yang <ioworker0@gmail.com>]

On Mon, Dec 2, 2024 at 8:47 PM Wenchao Hao <haowenchao22@gmail.com> wrote:
>
> Currently, large folio swap-in is supported, but we lack a method to
> analyze their success ratio. Similar to anon_fault_fallback, we introduce
> per-order mTHP swpin_fallback and swpin_fallback_charge counters for
> calculating their success ratio. The new counters are located at:
>
> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats/
>         swpin_fallback
>         swpin_fallback_charge
>
> Signed-off-by: Wenchao Hao <haowenchao22@gmail.com>

LGTM. Feel free to add:

Reviewed-by: Lance Yang <ioworker0@gmail.com>

Thanks,
Lance

> ---
> V3:
>  Update description about swpin_fallback and swpin_fallback_charge
>
> V2:
>  Introduce swapin_fallback_charge, which increments if it fails to
>  charge a huge page to memory despite successful allocation.
>
>  Documentation/admin-guide/mm/transhuge.rst | 10 ++++++++++
>  include/linux/huge_mm.h                    |  2 ++
>  mm/huge_memory.c                           |  6 ++++++
>  mm/memory.c                                |  2 ++
>  4 files changed, 20 insertions(+)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index 333958ef0d5f..156a03af0a88 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -591,6 +591,16 @@ swpin
>         is incremented every time a huge page is swapped in from a non-zswap
>         swap device in one piece.
>
> +swpin_fallback
> +       is incremented if swapin fails to allocate or charge a huge page
> +       and instead falls back to using huge pages with lower orders or
> +       small pages.
> +
> +swpin_fallback_charge
> +       is incremented if swapin fails to charge a huge page and instead
> +       falls back to using  huge pages with lower orders or small pages
> +       even though the allocation was successful.
> +
>  swpout
>         is incremented every time a huge page is swapped out to a non-zswap
>         swap device in one piece without splitting.
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index b94c2e8ee918..93e509b6c00e 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -121,6 +121,8 @@ enum mthp_stat_item {
>         MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
>         MTHP_STAT_ZSWPOUT,
>         MTHP_STAT_SWPIN,
> +       MTHP_STAT_SWPIN_FALLBACK,
> +       MTHP_STAT_SWPIN_FALLBACK_CHARGE,
>         MTHP_STAT_SWPOUT,
>         MTHP_STAT_SWPOUT_FALLBACK,
>         MTHP_STAT_SHMEM_ALLOC,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ab46ef718b44..d062b257376d 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -617,6 +617,8 @@ 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(zswpout, MTHP_STAT_ZSWPOUT);
>  DEFINE_MTHP_STAT_ATTR(swpin, MTHP_STAT_SWPIN);
> +DEFINE_MTHP_STAT_ATTR(swpin_fallback, MTHP_STAT_SWPIN_FALLBACK);
> +DEFINE_MTHP_STAT_ATTR(swpin_fallback_charge, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
>  DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
>  DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
>  #ifdef CONFIG_SHMEM
> @@ -637,6 +639,8 @@ static struct attribute *anon_stats_attrs[] = {
>  #ifndef CONFIG_SHMEM
>         &zswpout_attr.attr,
>         &swpin_attr.attr,
> +       &swpin_fallback_attr.attr,
> +       &swpin_fallback_charge_attr.attr,
>         &swpout_attr.attr,
>         &swpout_fallback_attr.attr,
>  #endif
> @@ -669,6 +673,8 @@ static struct attribute *any_stats_attrs[] = {
>  #ifdef CONFIG_SHMEM
>         &zswpout_attr.attr,
>         &swpin_attr.attr,
> +       &swpin_fallback_attr.attr,
> +       &swpin_fallback_charge_attr.attr,
>         &swpout_attr.attr,
>         &swpout_fallback_attr.attr,
>  #endif
> diff --git a/mm/memory.c b/mm/memory.c
> index d5a1b0a6bf1f..a44547600c02 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4189,8 +4189,10 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
>                         if (!mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
>                                                             gfp, entry))
>                                 return folio;
> +                       count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
>                         folio_put(folio);
>                 }
> +               count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
>                 order = next_order(&orders, order);
>         }
>
> --
> 2.45.0
>