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

[Lance Yang <ioworker0@gmail.com>]

On Sun, Nov 24, 2024 at 3:11 PM Barry Song <21cnbao@gmail.com> wrote:
>
> On Sun, Nov 24, 2024 at 2:56 PM Lance Yang <ioworker0@gmail.com> wrote:
> >
> > On Sat, Nov 23, 2024 at 9:17 PM Wenchao Hao <haowenchao22@gmail.com> wrote:
> > >
> > > On 2024/11/23 19:52, Lance Yang wrote:
> > > > On Sat, Nov 23, 2024 at 6:27 PM Barry Song <21cnbao@gmail.com> wrote:
> > > >>
> > > >> 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", not necessarily 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.
> > > >
> > > > Right, I clearly overlooked that ;)
> > > >
> > >
> > > Hi Lance and Barry,
> > >
> > > Do you think the following expression is clear? Compared to my original
> > > version, I’ve removed the word “huge” from the first line, and it now
> > > looks almost identical to anon_fault_fallback/anon_fault_fallback_charge.
> >
> > Well, that's fine with me. And let's see Barry's opinion as well ;)
>
> I still prefer Lance's version. The fallback path in it only needs to
> be adjusted to
> include huge pages with lower orders. In contrast, Wenchao's version feels less
> natural to me because "page swapin" sounds quite odd - we often hear
> "page fault,"
> but we have never encountered "page swapin."

Yeah, it makes sense to me ~

>
> So I mean:
>
>  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.

IHMO, much better and clearer than before ;)

Thank,
Lance

>
> >
> > Thanks,
> > Lance
> >
> > >
> > > swpin_fallback
> > >        is incremented if a 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.
> > >
> > > Thanks,
> > > Wencaho
> > >
> > > > Thanks,
> > > > Lance
> > > >
> > > >>
> > > >>>
> > > >>> 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