linux-kernel - Re: [PATCH v6 2/4] mm: add per-order mTHP anon_swpout and anon_swpout

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Date: Tue, 16 Apr 2024 20:16:42 +1200
From: Barry Song <21cnbao@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, cerasuolodomenico@...il.com, 
	chrisl@...nel.org, kasong@...cent.com, linux-kernel@...r.kernel.org, 
	peterx@...hat.com, ryan.roberts@....com, surenb@...gle.com, 
	v-songbaohua@...o.com, willy@...radead.org, yosryahmed@...gle.com, 
	yuzhao@...gle.com, corbet@....net
Subject: Re: [PATCH v6 2/4] mm: add per-order mTHP anon_swpout and
 anon_swpout_fallback counters

On Tue, Apr 16, 2024 at 8:14 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 12.04.24 13:48, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > This helps to display the fragmentation situation of the swapfile, knowing
> > the proportion of how much we haven't split large folios.  So far, we only
> > support non-split swapout for anon memory, with the possibility of
> > expanding to shmem in the future.  So, we add the "anon" prefix to the
> > counter names.
> >
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> > Cc: Chris Li <chrisl@...nel.org>
> > Cc: David Hildenbrand <david@...hat.com>
> > Cc: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> > Cc: Kairui Song <kasong@...cent.com>
> > Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
> > Cc: Peter Xu <peterx@...hat.com>
> > Cc: Ryan Roberts <ryan.roberts@....com>
> > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Yosry Ahmed <yosryahmed@...gle.com>
> > Cc: Yu Zhao <yuzhao@...gle.com>
> > ---
> >   include/linux/huge_mm.h | 2 ++
> >   mm/huge_memory.c        | 4 ++++
> >   mm/page_io.c            | 1 +
> >   mm/vmscan.c             | 3 +++
> >   4 files changed, 10 insertions(+)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index d4fdb2641070..7cd07b83a3d0 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -268,6 +268,8 @@ enum mthp_stat_item {
> >       MTHP_STAT_ANON_FAULT_ALLOC,
> >       MTHP_STAT_ANON_FAULT_FALLBACK,
> >       MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> > +     MTHP_STAT_ANON_SWPOUT,
> > +     MTHP_STAT_ANON_SWPOUT_FALLBACK,
> >       __MTHP_STAT_COUNT
> >   };
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index dfc38cc83a04..58f2c4745d80 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -555,11 +555,15 @@ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> >   DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
> >   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(anon_swpout, MTHP_STAT_ANON_SWPOUT);
> > +DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, MTHP_STAT_ANON_SWPOUT_FALLBACK);
> >
> >   static struct attribute *stats_attrs[] = {
> >       &anon_fault_alloc_attr.attr,
> >       &anon_fault_fallback_attr.attr,
> >       &anon_fault_fallback_charge_attr.attr,
> > +     &anon_swpout_attr.attr,
> > +     &anon_swpout_fallback_attr.attr,
> >       NULL,
> >   };
> >
> > diff --git a/mm/page_io.c b/mm/page_io.c
> > index a9a7c236aecc..46c603dddf04 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -217,6 +217,7 @@ static inline void count_swpout_vm_event(struct folio *folio)
> >               count_memcg_folio_events(folio, THP_SWPOUT, 1);
> >               count_vm_event(THP_SWPOUT);
> >       }
> > +     count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_SWPOUT);
> >   #endif
> >       count_vm_events(PSWPOUT, folio_nr_pages(folio));
> >   }
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index bca2d9981c95..49bd94423961 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1231,6 +1231,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> >                                               goto activate_locked;
> >                               }
> >                               if (!add_to_swap(folio)) {
> > +                                     int __maybe_unused order = folio_order(folio);
> > +
> >                                       if (!folio_test_large(folio))
> >                                               goto activate_locked_split;
> >                                       /* Fallback to swap normal pages */
> > @@ -1242,6 +1244,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> >                                                       THP_SWPOUT_FALLBACK, 1);
> >                                               count_vm_event(THP_SWPOUT_FALLBACK);
> >                                       }
> > +                                     count_mthp_stat(order, MTHP_STAT_ANON_SWPOUT_FALLBACK);
>
> Why the temporary variable for order?
>
> count_mthp_stat(folio_order(order),
>                  MTHP_STAT_ANON_SWPOUT_FALLBACK);
>
> ... but now I do wonder if we want to pass the folio to count_mthp_stat() ?

because we have called split_folio_to_list() before counting. that is also
why Ryan is using if (nr_pages >= HPAGE_PMD_NR) but not pmd_mappable.


>
> Anyhow
>
> Acked-by: David Hildenbrand <david@...hat.com>

thanks!

>
> --
> Cheers,
>
> David / dhildenb
>
Barry