Re: [PATCH] mm: move folio LRU helpers out of swap

[Baoquan He <bhe@redhat.com>]

On 04/08/26 at 10:20am, Barry Song wrote:
> On Wed, Apr 8, 2026 at 9:39 AM Baoquan He <bhe@redhat.com> wrote:
> >
> > On 04/07/26 at 10:22am, Johannes Weiner wrote:
> > > On Tue, Apr 07, 2026 at 07:00:02PM +0800, Jianyue Wu wrote:
> > > > All allocated folios are added into lru lists for later reclaim whether
> > > > they are file or anonymous folios. However those folio lru operation codes
> > > > are put in mm/swap.c which is not so appropriate. Because swap code is
> > > > only for anonymous folios.
> > >
> > > Ironically, the only thing that doesn't fit in this file is the swap
> > > stuff. The page_cluster & sysctl should be static in swap_state.c.
> > >
> > > The rest seems thematically relatively clean - infrastructure for
> > > managing folio lifetime. swap.c is not the best name for it, but short
> > > of finding a very clear improvement I'd just leave it alone.
> >
> > Can't agree more. We should move page_cluster & sysctl and swap_setup()
> > to mm/swap_state.c, and rename mm/swap.c to mm/folio_lru.c or something
> > like that.
> 
> Another issue is that many MM-internal items are placed in the
> top-level include/linux/swap.h, which is supposed to be used by
> code outside the MM subsystem as well.
> 
> For example, the following are actually MM-internal:
> 
> extern int vm_swappiness;
> swap_setup();
> workingset_*();
> try_to_free_pages();
> zone_reclaimable_pages();
> lruvec_lru_size();
> try_to_free_mem_cgroup_pages();
> ...

Ah, indeed. Seems we have been putting generic code related to reclaim into
swap.h|.c due to historic reason. From discussion, I think the below
three things are doable.

1) move page_cluster & sysctl and swap_setup() into mm/swap_state.c
because page_cluster is only used in mm/swap_state.c as Johannes
suggestd. And swap_setup() may need be renamed too?

2) rename mm/swap.c to mm/folio_lru.c or something like that to reflect
its real content;

3) Just Barry pointed out, move generic code related to reclaim out of
include/linux/swap.h  e.g move into mm/internal.h if they are only
called inside mm/ folder,

Thanks
Baoquan