Re: [PATCH v2 1/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[Miklos Szeredi <miklos@szeredi.hu>]

On Tue, 6 Jan 2026 at 15:34, David Hildenbrand (Red Hat)
<david@kernel.org> wrote:

> I don't recall all the details, but I think that we might end up holding
> the folio lock forever while the fuse user space daemon is supposed to
> fill the page with data; anybody trying to lock the folio would
> similarly deadlock.

Right.

> Maybe only compaction/migration is affected by that, hard to tell.

Can't imagine anything beyond actual I/O and folio logistics
(reclaim/compaction) that would want to touch the page lock.

I/O has the right to wait forever on the folio if the server is stuck,
that doesn't count as a deadlock.

The logistics functions are careful to use folio_trylock(), but they
could give a hint to fuse via a callback that they'd like to have this
particular folio.  In that case fuse would be free to cancel the read
and let the whole thing be retried with a new folio.

What we really need is a failing test case, the rest should be easy ;-)

> I'm not sure about temp buffers. During early discussions there were
> ideas about canceling writeback and instead marking the folio dirty
> again. I assume there is a non-trivial solution space left unexplored
> for now.

That might work combined with the suggested callback to fix the
compaction issue.

But I don't see how it would be a generic replacement for the tmp page code.

Thanks,
Miklos