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 10:17:31 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Cc: 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 16.04.24 10:14, David Hildenbrand 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() ?

.. 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