Re: [PATCH v2] mm: add per-order mTHP swap-in fallback/fallback_charge counters

[Barry Song <baohua@kernel.org>]

On Sat, Nov 23, 2024 at 10:36 AM Lance Yang <ioworker0@gmail.com> wrote:
>
> Hi Wenchao,
>
> On Sat, Nov 23, 2024 at 12:14 AM 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>
> > ---
> > 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 5034915f4e8e..9c07612281b5 100644
> > --- a/Documentation/admin-guide/mm/transhuge.rst
> > +++ b/Documentation/admin-guide/mm/transhuge.rst
> > @@ -561,6 +561,16 @@ swpin
> >         is incremented every time a huge page is swapped in from a non-zswap
> >         swap device in one piece.
> >
>
> Would the following be better?
>
> +swpin_fallback
> +       is incremented if a huge page swapin fails to allocate or charge
> +       it and instead falls back to using small pages.
>
> +swpin_fallback_charge
> +       is incremented if a huge page swapin fails to charge it and instead
> +       falls back to using small pages even though the allocation was
> +       successful.

much better, but it is better to align with "huge pages with
lower orders or small pages."

anon_fault_fallback
is incremented if a page fault fails to allocate or charge
a huge page and instead falls back to using huge pages with
lower orders or small pages.

anon_fault_fallback_charge
is incremented if a page fault 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.


>
> Thanks,
> Lance
>
> > +swpin_fallback
> > +       is incremented if a huge page 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 a page 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 ee335d96fc39..46749dded1c9 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 209885a4134f..774dfd309cfe 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
> >

Thanks
Barry