linux-kernel - Re: LTP write03 writev07 xfs failures

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Date:   Tue, 28 Feb 2017 06:04:55 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Brian Foster <bfoster@...hat.com>
Cc:     Xiong Zhou <xzhou@...hat.com>, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: LTP write03 writev07 xfs failures

On Mon, Feb 27, 2017 at 03:13:35PM -0500, Brian Foster wrote:
> After playing around a bit, I don't think using i_size is the right
> approach either. It just exacerbates the original problem on buffered
> writes into sparse files. We can end up leaving around however many
> delalloc blocks we've allocated.
> 
> I think we need a way to differentiate preexisting (previously written)
> delalloc blocks from those allocated and unused by the current write. We
> might be able to do that by looking at the pagecache, but I think that
> means looking at the buffer state to make sure we handle sub-page block
> sizes correctly. I.e., make *_iomap_end_delalloc() punch out all
> delalloc blocks in the non-written range that are either not page backed
> or not dirty+delalloc buffer backed. Hm?

That sounds ugly, but right off my mind I see no other way.  I'll need
to take a look at what the old pre-iomap code did there, as I think
none of these issues happened there.