Re: NFS directio

[Chuck Lever <cel@citi.umich.edu>]

Trond Myklebust wrote:
> 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().

that's correct.  this was just an arbitrary limit to prevent type 
overflows (namely the atomic_t's were only 24 bits on some platforms).

-- 
corporate:	<cel at netapp dot com>
personal:	<chucklever at bigfoot dot com>


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