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From: Alex Elder <aelder@sgi.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 8/8] xfs: serialise unaligned direct IOs
Date: Tue, 04 Jan 2011 19:55:15 -0600	[thread overview]
Message-ID: <1294192515.2485.729.camel@doink> (raw)
In-Reply-To: <1294116518-14908-9-git-send-email-david@fromorbit.com>

On Tue, 2011-01-04 at 15:48 +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> When two concurrent unaligned, non-overlapping direct IOs are issued
> to the same block, the direct Io layer will race to zero the block.
> The result is that one of the concurrent IOs will overwrite data
> written by the other IO with zeros. This is demonstrated by the
> xfsqa test 240.
> 
> To avoid this problem, serialise all unaligned direct IOs to an
> inode with a big hammer. We need a big hammer approach as we need to
> serialise AIO as well, so we can't just block writes on locks.
> Hence, the big hammer is calling xfs_ioend_wait() while holding out
> other unaligned direct IOs from starting.
> 
> We don't bother trying to serialised aligned vs unaligned IOs as
> they are overlapping IO and the result of concurrent overlapping IOs
> is undefined - the result of either IO is a valid result so we let
> them race. Hence we only penalise unaligned IO, which already has a
> major overhead compared to aligned IO so this isn't a major problem.

Wow, after the rest of this series it gets easy!
Looks good.

Reviewed-by: Alex Elder <aelder@sgi.com>

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/linux-2.6/xfs_file.c |   28 ++++++++++++++++++++++++----
>  1 files changed, 24 insertions(+), 4 deletions(-)


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  reply	other threads:[~2011-01-05  1:53 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-04  4:48 [PATCH 0/8] xfs: prevent corruption due to overlapping AIO DIO V2 Dave Chinner
2011-01-04  4:48 ` [PATCH 1/8] xfs: ensure sync write errors are returned Dave Chinner
2011-01-05  1:53   ` Alex Elder
2011-01-07  8:45   ` Christoph Hellwig
2011-01-07  9:07     ` Dave Chinner
2011-01-04  4:48 ` [PATCH 2/8] xfs: factor common post-write isize handling code Dave Chinner
2011-01-05  1:54   ` Alex Elder
2011-01-04  4:48 ` [PATCH 4/8] xfs: introduce xfs_rw_lock() helpers for locking the inode Dave Chinner
2011-01-05  1:54   ` Alex Elder
2011-01-05  7:55     ` Dave Chinner
2011-01-04  4:48 ` [PATCH 5/8] xfs: split direct IO write path from xfs_file_aio_write Dave Chinner
2011-01-05  1:54   ` Alex Elder
2011-01-05  7:36     ` Dave Chinner
2011-01-07  8:58   ` Christoph Hellwig
2011-01-07  9:21     ` Dave Chinner
2011-01-04  4:48 ` [PATCH 6/8] xfs: split buffered " Dave Chinner
2011-01-05  1:55   ` Alex Elder
2011-01-04  4:48 ` [PATCH 7/8] xfs: factor common write setup code Dave Chinner
2011-01-05  1:55   ` Alex Elder
2011-01-07  8:53   ` Christoph Hellwig
2011-01-07  9:20     ` Dave Chinner
2011-01-04  4:48 ` [PATCH 8/8] xfs: serialise unaligned direct IOs Dave Chinner
2011-01-05  1:55   ` Alex Elder [this message]
2011-01-05  1:53 ` [PATCH 0/8] xfs: prevent corruption due to overlapping AIO DIO V2 Alex Elder
  -- strict thread matches above, loose matches on Subject: below --
2011-01-07 11:30 [PATCH 0/8] xfs: prevent corruption due to overlapping AIO DIO V3 Dave Chinner
2011-01-07 11:30 ` [PATCH 8/8] xfs: serialise unaligned direct IOs Dave Chinner
2011-01-10 19:26   ` Christoph Hellwig
2011-01-10 23:37 [PATCH 0/8] xfs: prevent corruption due to overlapping AIO DIO V4 Dave Chinner
2011-01-10 23:37 ` [PATCH 8/8] xfs: serialise unaligned direct IOs Dave Chinner

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