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From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org, hch@infradead.org
Subject: Re: [PATCH 2/2] xfs: relax unwritten writeback overhead under some circumstances
Date: Thu, 16 Jan 2020 08:49:00 -0800
Message-ID: <20200116164900.GB4593@infradead.org> (raw)
In-Reply-To: <157915535801.2406747.10502356876965505327.stgit@magnolia>

On Wed, Jan 15, 2020 at 10:15:58PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> In the previous patch, we solved a stale disk contents exposure problem
> by forcing the delalloc write path to create unwritten extents, write
> the data, and convert the extents to written after writeback completes.
> 
> This is a pretty huge hammer to use, so we'll relax the delalloc write
> strategy to go straight to written extents (as we once did) if someone
> tells us to write the entire file to disk.  This reopens the exposure
> window slightly, but we'll only be affected if writeback completes out
> of order and the system crashes during writeback.
> 
> Because once again we can map written extents past EOF, we also
> enlarge the writepages window downward if the window is beyond the
> on-disk size and there are written extents after the EOF block.  This
> ensures that speculative post-EOF preallocations are not left uncovered.

This does sound really sketchy.  Do you have any performance numbers
justifying something this nasty?

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  6:15 [PATCH 0/2] xfs: fix stale disk exposure after crash Darrick J. Wong
2020-01-16  6:15 ` [PATCH 1/2] xfs: force writes to delalloc regions to unwritten Darrick J. Wong
2020-01-16 16:47   ` Christoph Hellwig
2020-01-16 23:16     ` Darrick J. Wong
2020-01-19 20:49   ` Dave Chinner
2020-01-16  6:15 ` [PATCH 2/2] xfs: relax unwritten writeback overhead under some circumstances Darrick J. Wong
2020-01-16 16:49   ` Christoph Hellwig [this message]
2020-01-16 23:15     ` Darrick J. Wong
2020-01-16 16:49 ` [PATCH 0/2] xfs: fix stale disk exposure after crash Christoph Hellwig
2020-01-16 23:00   ` Darrick J. Wong

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