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Date:   Wed, 2 Nov 2022 01:25:52 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Brian Foster <bfoster@redhat.com>
Cc:     linux-xfs@vger.kernel.org
Subject: Re: [PATCH] xfs: redirty eof folio on truncate to avoid filemap flush
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On Fri, Oct 28, 2022 at 02:26:47PM -0400, Brian Foster wrote:
> index 91ee0b308e13..14a9734b2838 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -899,7 +899,8 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
>  	loff_t written = 0;
>  
>  	/* already zeroed?  we're done. */
> -	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
> +	if ((srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN) &&
> +	    !(srcmap->flags & IOMAP_F_TRUNC_PAGE))

As mentioned elsewere in the thread I think we can just move the
filemap_range_needs_writeback here, which removes the need for
IOMAP_F_TRUNC_PAGE.

> +static int
> +__iomap_zero_range(struct iomap_iter *iter, bool *did_zero,
> +		   const struct iomap_ops *ops)
> +{
> +	int ret;
> +
> +	while ((ret = iomap_iter(iter, ops)) > 0)
> +		iter->processed = iomap_zero_iter(iter, did_zero);
> +	return ret;
> +}

I'd be tempted to just duplicate this two line loop instead of adding
such a tivial helper, but that's just a matter of taste.