From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: NFS directio
Date: Thu, 30 Mar 2006 11:03:32 -0500
Message-ID: <1143734612.8093.8.camel@lade.trondhjem.org>
References: <20060330151544.GA11915@suse.de>
Mime-Version: 1.0
Content-Type: text/plain
Cc: nfs@lists.sourceforge.net
To: Olaf Kirch <okir@suse.de>
In-Reply-To: <20060330151544.GA11915@suse.de>
Sender: nfs-admin@lists.sourceforge.net
Errors-To: nfs-admin@lists.sourceforge.net

On Thu, 2006-03-30 at 17:15 +0200, Olaf Kirch wrote:
> In recent kernels, NFS direct IO limits the size of a request to
> 4096 pages, ie 16M on most platforms. This causes growisofs from the
> dvd+rw-tools package (http://fy.chalmers.se/~appro/linux/DVD+RW/) to fail.
> Its builtin "dd" style function uses 32M buffers by default.
> 
> It puzzled me a lot that it is returning -EFBIG, which means "file too
> big". At least that should be EINVAL, I think. EFBIG should be reserved
> for problems related to largefile support, IMO.
> 
> We can easily work around the problem by restricting the buffer size
> growisofs uses on NFS, but that feels strange. I think the right way
> would be to increase MAX_DIRECTIO_SIZE, and if someone submits a bigger
> request, to loop and do that in MAX_DIRECTIO_SIZE chunks.
> 
> Comments?

MAX_DIRECTIO_SIZE is gone from Linus' tree. I don't think we have any
limits on the size of the buffer that users can feed to us apart from
those set by mm/filemap.c:generic_write_checks().

Cheers,
  Trond


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