Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, 3 Jan 2025 at 21:31, David Hildenbrand <david@redhat.com> wrote:
> In any case, having movable pages be turned unmovable due to persistent
> writaback is something that must be fixed, not worked around. Likely a
> good topic for LSF/MM.

Yes, this seems a good cross fs-mm topic.

So the issue discussed here is that movable pages used for fuse
page-cache cause a problems when memory needs to be compacted. The
problem is either that

 - the page is skipped, leaving the physical memory block unmovable

 - the compaction is blocked for an unbounded time

While the new AS_WRITEBACK_INDETERMINATE could potentially make things
worse, the same thing happens on readahead, since the new page can be
locked for an indeterminate amount of time, which can also block
compaction, right?

What about explicitly opting fuse cache pages out of compaction by
allocating them form ZONE_UNMOVABLE?

Thanks,
Miklos