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SubjectRe: another nfs puzzle
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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