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

[Lance Yang]

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 :)

[1] 
https://lore.kernel.org/linux-mm/63797977-1c18-4885-8099-f5c21c80da39@xxxxxxxxx/

Cheers, Lance