Re: [PATCH v5 9/9] mm: switch deferred split shrinker to list_lru

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Jun 01, 2026 at 09:21:35PM +0800, Lance Yang wrote:
> 
> On Wed, May 27, 2026 at 04:45:16PM -0400, Johannes Weiner wrote:
> [...]
> >diff --git a/mm/swap_state.c b/mm/swap_state.c
> >index 04f5ce992401..9c3a5cf99778 100644
> >--- a/mm/swap_state.c
> >+++ b/mm/swap_state.c
> >@@ -465,6 +465,16 @@ static struct folio *__swap_cache_alloc(struct swap_cluster_info *ci,
> > 		return ERR_PTR(-ENOMEM);
> > 	}
> > 
> 
> Shouldn't this be limited to anon swapin?
> 
> e.g. vmf && vma_is_anonymous(vmf->vma)
> 
> >+	if (order > 1 && folio_memcg_alloc_deferred(folio)) {
> 
> __swap_cache_alloc() is also used by shmem direct swapin, so shmem can
> get here too when handling a large swap entry:
> 
> shmem_get_folio_gfp()
>   shmem_swapin_folio()
>     shmem_swap_alloc_folio()
>       swapin_sync()
>         swap_cache_alloc_folio()
>           __swap_cache_alloc()
>             folio_memcg_alloc_deferred()

Good catch, I think you're right. I shouldn't have dismissed that
branch due to "/* Direct swapin skipping swap cache & readahead */"

> @Baolin please correct me if I got it wrong :)
> 
> folio_memcg_alloc_deferred() itself doesn't filter shmem out either; it
> only allocates the memcg list_lru metadata for deferred_split_lru:
> 
> int folio_memcg_alloc_deferred(struct folio *folio)
> {
> 	if (mem_cgroup_disabled())
> 		return 0;
> 	return folio_memcg_list_lru_alloc(folio, &deferred_split_lru, GFP_KERNEL);
> }
> 
> Since deferred_split_lru only queues anon large folios, doing this for
> shmem swapin doesn't buy us anything :)

Yes, agreed. I don't think it's a big deal / show stopper in terms of
user-visible effect, but of course still worth fixing.

I'll send a follow-up patch.