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Date:   Wed, 16 Oct 2019 10:10:09 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Dave Chinner <david@fromorbit.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 09/12] iomap: lift the xfs writeback code to iomap
Message-ID: <20191016081009.GA24284@lst.de>
References: <20191015154345.13052-1-hch@lst.de> <20191015154345.13052-10-hch@lst.de> <20191015220721.GC16973@dread.disaster.area>
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On Wed, Oct 16, 2019 at 09:07:21AM +1100, Dave Chinner wrote:
> > +/*
> > + * We implement an immediate ioend submission policy here to avoid needing to
> > + * chain multiple ioends and hence nest mempool allocations which can violate
> > + * forward progress guarantees we need to provide. The current ioend we are
> > + * adding blocks to is cached on the writepage context, and if the new block
> 
> adding pages to ... , and if the new block mapping

So reviewing this comment I disagree with the change.  We add on a per-
block basis to the ioend, not a per-page one.  Similar for the second 
one it is the block that needs to append (which is defined by the
mapping, but still..).