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

[David Hildenbrand (Arm)]

On 6/3/26 04:00, Lance Yang wrote:
> 
> 
> On 2026/6/3 04:37, Andrew Morton wrote:
>> On Tue,  2 Jun 2026 12:34:53 +0800 Lance Yang <lance.yang@xxxxxxxxx> 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.
>>>
>>> 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)
>>
>> Should this be handled as a fix against hannes's "mm: switch deferred
>> split shrinker to list_lru"?
> 
> Hmm ... I noticed this while looking at Johannes' work, but the
> behavior is older than that ...
> 
> We also discussed the Fixes tag earlier[1] and decided to leave it
> out. There is no missed reclaim, only some extra reclaim work :)

Right, I conclude that this can be a separate patch on top.

-- 
Cheers,

David