Re: [PATCH 1/1] mm/thp: clear deferred split shrinker bits when queues drain

[David Hildenbrand (Arm)]

On 6/2/26 06:38, Lance Yang wrote:
> Sorry, I missed Johannes in Cc ...
> 
> On 2026/6/2 12:34, Lance Yang wrote:
>> From: Lance Yang <lance.yang@xxxxxxxxx>
>>
>> deferred_split_count() returns the raw list_lru count. When the per-memcg,
>> per-node list is empty, that count is 0.
>>
>> That skips scanning, but it does not tell memcg reclaim that the shrinker
>> is empty. shrink_slab_memcg() only clears the memcg shrinker bit when the
>> count callback reports SHRINK_EMPTY.

What's the effect of that? Would we consider it a fix that we'd want to backport?

>>
>> Return SHRINK_EMPTY for an empty deferred split list, so the bit can be
>> cleared once the queue has drained.
>>
>> Signed-off-by: Lance Yang <lance.yang@xxxxxxxxx>
>> ---
>>   mm/huge_memory.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 72f6caf0fec6..62d598290c3b 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -4397,7 +4397,10 @@ void deferred_split_folio(struct folio *folio, bool
>> partially_mapped)
>>   static unsigned long deferred_split_count(struct shrinker *shrink,
>>           struct shrink_control *sc)
>>   {
>> -    return list_lru_shrink_count(&deferred_split_lru, sc);
>> +    unsigned long count;
>> +
>> +    count = list_lru_shrink_count(&deferred_split_lru, sc);
>> +    return count ?: SHRINK_EMPTY;
>>   }
>>     static bool thp_underused(struct folio *folio)
> 

This is against Johannes' work, right?

If this is a fix, likely it would be fixing 87eaceb3faa5 ("mm: thp: make
deferred split shrinker memcg aware"), right?

-- 
Cheers,

David