linux-ext4 - Re: [RFC v3 5/7] iomap: Get page in page

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Date:   Fri, 23 Dec 2022 07:07:38 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: [RFC v3 5/7] iomap: Get page in page_prepare handler

On Fri, Dec 16, 2022 at 04:06:24PM +0100, Andreas Gruenbacher wrote:
> Change the iomap ->page_prepare() handler to get and return a locked
> folio instead of doing that in iomap_write_begin().  This allows to
> recover from out-of-memory situations in ->page_prepare(), which
> eliminates the corresponding error handling code in iomap_write_begin().
> The ->page_done() handler is now not called with a NULL folio anymore.

Ah, okay - this is the other half of what I asked for earlier, so
we're aligned.  Sorry for the noise earlier.  I'd still prefer the
naming I suggest, though.

> +	if (page_ops && page_ops->page_prepare)
> +		folio = page_ops->page_prepare(iter, pos, len);
> +	else
> +		folio = iomap_folio_prepare(iter, pos);
> +	if (IS_ERR_OR_NULL(folio)) {
> +		if (!folio)
> +			return (iter->flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOMEM;
> +		return PTR_ERR(folio);
>  	}

Maybe encapsulate this in a iomap_get_folio wrapper just to keep the
symmetry with the done side.