On Mon, Jun 26, 2023 at 09:12:07PM -0700, Christoph Hellwig wrote:
> > + if (folio_test_writeback(folio)) {
> > + if (wbc->sync_mode != WB_SYNC_NONE)
> > + folio_wait_writeback(folio);
> > + else
> > + return false;
> > + }
>
> Please reorder this to avoid the else and return earlier while you're
> at it:
>
> if (folio_test_writeback(folio)) {
> if (wbc->sync_mode == WB_SYNC_NONE)
> return false;
> folio_wait_writeback(folio);
> }
Sure, that makes sense.
> (that's what actually got me started on my little cleanup spree while
> checking some details of the writeback waiting..)
This might be a good point to share that I'm considering (eventually)
not taking the folio lock here.
My plan looks something like this (not fully baked):
truncation (and similar) paths currently lock the folio, They would both
lock the folio _and_ claim that they were doing writeback on the folio.
Filesystems would receive the folio from the writeback iterator with
the writeback flag already set.
This allows, eg, folio mapping/unmapping to take place completely
independent of writeback. That seems like a good thing; I can't see
why the two should be connected.
> > + BUG_ON(folio_test_writeback(folio));
> > + if (!folio_clear_dirty_for_io(folio))
> > + return false;
> > +
> > + return true;
>
> ..
>
> return folio_clear_dirty_for_io(folio);
>
> ?
I did consider that, but there's a nice symmetry to the code the way it's
currently written, and that took precedence in my mind over "fewer lines
of code". There's nothing intrinsic about folio_clear_dirty_for_io()
being the last condition to be checked (is there? We have to
redirty_for_io if we decide to not start writeback), so it seemed to
make sense to leave space to add more conditions.
