linux-ext4 - Re: [PATCH v7 21/24] iomap: Restructure iomap_readpages

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Date:   Mon, 24 Feb 2020 17:49:49 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        ocfs2-devel@....oracle.com, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v7 21/24] iomap: Restructure iomap_readpages_actor

On Mon, Feb 24, 2020 at 02:17:49PM -0800, Christoph Hellwig wrote:
> On Thu, Feb 20, 2020 at 08:24:04AM -0800, Matthew Wilcox wrote:
> > On Thu, Feb 20, 2020 at 07:47:41AM -0800, Christoph Hellwig wrote:
> > > On Wed, Feb 19, 2020 at 01:01:00PM -0800, Matthew Wilcox wrote:
> > > > From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > > > 
> > > > By putting the 'have we reached the end of the page' condition at the end
> > > > of the loop instead of the beginning, we can remove the 'submit the last
> > > > page' code from iomap_readpages().  Also check that iomap_readpage_actor()
> > > > didn't return 0, which would lead to an endless loop.
> > > 
> > > I'm obviously biassed a I wrote the original code, but I find the new
> > > very much harder to understand (not that the previous one was easy, this
> > > is tricky code..).
> > 
> > Agreed, I found the original code hard to understand.  I think this is
> > easier because now cur_page doesn't leak outside this loop, so it has
> > an obvious lifecycle.
> 
> I really don't like this patch, and would prefer if the series goes
> ahead without it, as the current sctructure works just fine even
> with the readahead changes.

Dave Chinner specifically asked me to do it this way, so please fight
amongst yourselves.