Re: [PATCH v3 1/1] iomap: fix readahead folio access after folio_end_read()

[Matthew Wilcox <willy@infradead.org>]

On Thu, Jan 22, 2026 at 11:50:18AM -0800, Joanne Koong wrote:
> On Thu, Jan 22, 2026 at 8:51 AM Matthew Wilcox <willy@infradead.org> wrote:
> > This is so complicated.  I think you made your life harder by adding the
> > bias to read_bytes_pending.  What if we just rip most of this out ...
> 
> I don't think we can rip this out because when the read starts,
> ifs->read_bytes_pending gets set to the folio size, but if there are
> already some uptodate ranges in the folio, the filesystem IO helper
> will not be reading in the entire folio size, which means we still
> need all this logic to decrement ifs->read_bytes_pending by the bytes
> not read in by the IO helper and to end the folio read.

Well, the patch as-is doesn't work (squinting at it now to see
what I missed ...), but that's not an insurmountable problem.
If we find already-uptodate blocks in the folio, we can just call
iomap_finish_folio_read() for them without starting I/O.  That's very
much a corner case, so we need not try hard for efficiency (eg skipping
the ifs_set_range_uptodate() call).