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Date:   Thu, 23 Mar 2023 03:26:43 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Ritesh Harjani <ritesh.list@gmail.com>
Cc:     Theodore Tso <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 04/31] ext4: Convert ext4_finish_bio() to use folios
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On Mon, Mar 06, 2023 at 02:40:55PM +0530, Ritesh Harjani wrote:
> "Matthew Wilcox (Oracle)" <willy@infradead.org> writes:
> 
> > Prepare ext4 to support large folios in the page writeback path.
> 
> Sure. I am guessing for ext4 to completely support large folio
> requires more work like fscrypt bounce page handling doesn't
> yet support folios right?
> 
> Could you please give a little background on what all would be required
> to add large folio support in ext4 buffered I/O path?
> (I mean ofcourse other than saying move ext4 to iomap ;))
> 
> What I was interested in was, what other components in particular for
> e.g. fscrypt, fsverity, ext4's xyz component needs large folio support?
> 
> And how should one go about in adding this support? So can we move
> ext4's read path to have large folio support to get started?
> Have you already identified what all is missing from this path to
> convert it?

Honestly, I don't know what else needs to be done beyond this patch
series.  I can point at some stuff and say "This doesn't work", but in
general, you have to just enable it and see what breaks.  A lot of the
buffer_head code is not large-folio safe right now, so that's somewhere
to go and look.  Or maybe we "just" convert to iomap, and never bother
fixing the bufferhead code for large folios.

> > Also set the actual error in the mapping, not just -EIO.
> 
> Right. I looked at the history and I think it always just had EIO.
> I think setting the actual err in mapping_set_error() is the right thing
> to do here.
> 
> >
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> w.r.t this patch series. I reviewed the mechanical changes & error paths
> which converts ext4 ext4_finish_bio() to use folio.
> 
> The changes looks good to me from that perspective. Feel free to add -
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Thanks!