linux-kernel - Re: [PATCH v14 106/138] iomap: Convert iomap_do

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Date:   Fri, 16 Jul 2021 03:06:50 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v14 106/138] iomap: Convert iomap_do_writepage to use a
 folio

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).