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

[David Hildenbrand]

On 16.04.24 10:14, David Hildenbrand wrote:
> On 12.04.24 13:48, Barry Song wrote:
> > From: Barry Song <v-songbaohua@xxxxxxxx>
> >
> > 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@xxxxxxxx>
> > Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> > Cc: Chris Li <chrisl@xxxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
> > Cc: Kairui Song <kasong@xxxxxxxxxxx>
> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > Cc: Peter Xu <peterx@xxxxxxxxxx>
> > Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> > Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> > Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
> > ---
> >    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() ?

.. and now realizing, that that doesn't make sense if we fail to 
allocate the folio in the first place. So all good.

--
Cheers,

David / dhildenb