linux-kernel - Re: [PATCH v2 5/5] mm: add per-order mTHP swpin

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Date: Wed, 17 Apr 2024 09:38:22 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org,  linux-mm@...ck.org,
  baolin.wang@...ux.alibaba.com,  chrisl@...nel.org,  david@...hat.com,
  hanchuanhua@...o.com,  hannes@...xchg.org,  hughd@...gle.com,
  kasong@...cent.com,  ryan.roberts@....com,  surenb@...gle.com,
  v-songbaohua@...o.com,  willy@...radead.org,  xiang@...nel.org,
  yosryahmed@...gle.com,  yuzhao@...gle.com,  ziy@...dia.com,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] mm: add per-order mTHP swpin_refault counter

Barry Song <21cnbao@...il.com> writes:

> On Wed, Apr 17, 2024 at 8:47 AM Huang, Ying <ying.huang@...el.com> wrote:
>>
>> Barry Song <21cnbao@...il.com> writes:
>>
>> > From: Barry Song <v-songbaohua@...o.com>
>> >
>> > 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@...o.com>
>> > ---
>> >  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,
>>
>> This is different from the refault concept used in other place in mm
>> subystem.  Please check the following code
>>
>>         if (shadow)
>>                 workingset_refault(folio, shadow);
>>
>> in __read_swap_cache_async().
>
> right. it is slightly different as refault can also cover the case folios
> have been entirely released and a new page fault happens soon
> after it.
> Do you have a better name for this?
> MTHP_STAT_ANON_SWPIN_UNDER_RECLAIM
> or
> MTHP_STAT_ANON_SWPIN_RECLAIMING ?

TBH, I don't think we need this counter.  It's important for you during
implementation.  But I don't think it's important for end users.

--
Best Regards,
Huang, Ying

>>
>> >       __MTHP_STAT_COUNT
>> >  };
>>
>> --
>> Best Regards,
>> Huang, Ying
>>
>> > 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);
>> >       }
>> >
>> >  check_pte: