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Re: XFS issue under kernel

To: Sławomir Nowakowski <nailman23@xxxxxxxxx>
Subject: Re: XFS issue under kernel
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 28 Aug 2008 10:20:05 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <50ed5c760808271109u4dee0311ha7cf2c1e7cae31dd@xxxxxxxxxxxxxx>
Mail-followup-to: Sławomir Nowakowski <nailman23@xxxxxxxxx>, xfs@xxxxxxxxxxx
References: <50ed5c760808220303p37e03e8dge5b868a572374e0b@xxxxxxxxxxxxxx> <20080823010524.GM5706@disturbed> <50ed5c760808250408o44aeaf07me262eab8da8340ba@xxxxxxxxxxxxxx> <20080826014133.GS5706@disturbed> <50ed5c760808260553i7def5e93qb0bcb4d2206a4a38@xxxxxxxxxxxxxx> <20080827005243.GB5706@disturbed> <50ed5c760808271109u4dee0311ha7cf2c1e7cae31dd@xxxxxxxxxxxxxx>
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On Wed, Aug 27, 2008 at 08:09:18PM +0200, Sławomir Nowakowski wrote:
> Dear Dave,
> We really apreciate your help..
> In the realtion to previous correspondations about differences between
> implementation of kernels and we'd like to ask
> some questions.
> We was based on git repository:
> git://git.kernel.org
> We have reverted some changes for XFS in kernel. We have
> usedf 3 commits:
> - 94E1E99F11... (SGI-PV: 964468)
> - 4BE536DEBE... (SGI-PV: 955674)
> - 4CA488EB4...  (SGI-PV: 971186)
> With these changes we have created patch for kernel. This
> patch should eliminate additional reservation of disk space in XFS
> file system. Our intention was to get similarity space of disk between
> and kernels.

After removing the reservation with xfs_io (the big difference), I
don't see why you need to hack the kernel as well. Have you got
such little margin in your filesystem provisioning that you can't
spare 4 blocks per AG?

> Does patch that is attached to this mail do everything properly?

Don't know. You've taken away a bunch of reserved blocks other
code relies on existing for correct operation at ENOSPC. Given
that you are doing this because you are running so close to
ENOSPC there's a good chance that you've broken something.

I don't have the time (or the desire) to analyse the impact of the
changes being made, but I bet that the XFSQA tests that exercise
behaviour at ENOSPC will start to deadlock again...

> Is it
> 100% compatibe with XFS API?

You've changed statfs. You'll have to make sure it reports
the correct thing in all cases (there's an XFSQA test for this).


Dave Chinner

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