Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 16 Jul 2021 03:06:50 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v14 106/138] iomap: Convert iomap_do_writepage to use a
 folio
Message-ID: <YPDpunndhcBUeS+U@casper.infradead.org>
References: <20210715033704.692967-1-willy@infradead.org>
 <20210715033704.692967-107-willy@infradead.org>
 <20210715220505.GQ22357@magnolia>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210715220505.GQ22357@magnolia>
Precedence: bulk

On Thu, Jul 15, 2021 at 03:05:05PM -0700, Darrick J. Wong wrote:
> On Thu, Jul 15, 2021 at 04:36:32AM +0100, Matthew Wilcox (Oracle) wrote:
> > Writeback an entire folio at a time, and adjust some of the variables
> > to have more familiar names.
> > @@ -1398,16 +1397,15 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> >  static int
> >  iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
> 
> I imagine at some point this will become iomap_do_writefolio and ther
> will be some sort of write_cache_folios() call?  Or the equivalent
> while(get_next_folio_to_wrote()) iomap_write_folio(); type loop?

I hadn't quite got as far as planning out what to do next with a
replacement for write_cache_pages().  At a minimum, that function is
going to work on folios -- it does anyway; we don't tag tail pages in
the xarray, so the tagged lookup done by write_cache_pages() only finds
folios.  So everything we do with a page there is definitely looking at
a folio.

I want to get a lot more filesystems converted to use folios before I
undertake the write_cache_pages() interface overhaul (and I'll probably
think of several things to do to it at the same time -- like working on
a batch of pages all at once instead of calling one indirect function
per folio).