Message-ID: <4396EF50.30201@redhat.com>
Date: Wed, 07 Dec 2005 09:18:56 -0500
From: Peter Staubach <staubach@redhat.com>
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To: Trond Myklebust <trond.myklebust@fys.uio.no>
CC: Kenny Simpson <theonetruekenny@yahoo.com>, linux-kernel@vger.kernel.org
Subject: Re: another nfs puzzle
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Trond Myklebust wrote:

>On Wed, 2005-12-07 at 09:01 -0500, Peter Staubach wrote:
>  
>
>>Kenny Simpson wrote:
>>
>>    
>>
>>>Hi again,
>>> I am seeing some odd behavior with O_DIRECT.  If a file opened with O_DIRECT has a page mmap'd,
>>>and the file is extended via pwrite, then the mmap'd region seems to get lost - i.e. it neither
>>>takes up system memory, nor does it get written out.
>>> 
>>>
>>>      
>>>
>>I don't think that I understand why or how the kernel allows a file,
>>which was opened with O_DIRECT, to be mmap'd.  The use of O_DIRECT
>>implies no caching and mmap implies the use of caching.
>>    
>>
>
>In this context it doesn't matter whether or not the you use the same
>file descriptor. The problem is the same if my process opens the file
>for O_DIRECT and then your process open it for normal I/O, and mmaps it.
>

Yup, same problem.  Why is this allowed?  Does it really work correctly?

    Thanx...

       ps
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