linux-kernel - Re: [PATCH 07/12] writeback: Factor writeback_iter_init() out of write_cache

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Date:   Tue, 27 Jun 2023 12:08:30 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 07/12] writeback: Factor writeback_iter_init() out of
 write_cache_pages()

On Mon, Jun 26, 2023 at 09:31:56PM -0700, Christoph Hellwig wrote:
> On Mon, Jun 26, 2023 at 09:30:07PM -0700, Christoph Hellwig wrote:
> > On Mon, Jun 26, 2023 at 06:35:16PM +0100, Matthew Wilcox (Oracle) wrote:
> > > +	for (folio = writeback_iter_init(mapping, wbc);
> > > +	     folio;
> > > +	     folio = writeback_get_next(mapping, wbc)) {
> > 
> > Ok that's another way to structure it.  Guess I should look over the
> > whole series first..

Perhaps ... it's a little hard to decide which of your comments
are worth replying to, and which are obviated by later realisations.

> That beeing said.  Given that writeback_iter_init calls 
> writeback_get_next anyway,
> 
> 	writeback_iter_init(mapping, wbc);
> 	while ((folio = writeback_get_next(mapping, wbc)))
> 
> still feels a little easier to follow to be.  No hard feelings either
> way, just an observation.

I had it structured that way originally, but we need to pass in 'error'
to the get_next, and it's better if we also pass in 'folio', which means
that the user then needs to initialise error to 0 and folio to NULL
before using the macro, and that all felt a bit "You're holding it wrong".