linux-kernel - Re: [PATCH 1/3] fs: allow short direct-io reads to be completed via buffered IO V2

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Message-ID: <20100506211012.GD2997@infradead.org>
Date:	Thu, 6 May 2010 17:10:12 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Josef Bacik <josef@...hat.com>
Cc:	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] fs: allow short direct-io reads to be completed
	via buffered IO V2

On Thu, May 06, 2010 at 03:00:13PM -0400, Josef Bacik wrote:
> V1->V2: Check to see if our current ppos is >= i_size after a short DIO read,
> just in case it was actually a short read and we need to just return.
> 
> This is similar to what already happens in the write case.  If we have a short
> read while doing O_DIRECT, instead of just returning, fallthrough and try to
> read the rest via buffered IO.  BTRFS needs this because if we encounter a
> compressed or inline extent during DIO, we need to fallback on buffered.  If the
> extent is compressed we need to read the entire thing into memory and
> de-compress it into the users pages.  I have tested this with fsx and everything
> works great.  Thanks,

This seems safe to me, but I'm a bit worried about potential breakages.
Did you test this with xfsqa on xfs and ext3/4 to make sure there are
no regressions?

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