From owner-freebsd-hackers  Tue Jun 30 18:57:39 1998
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Date: Tue, 30 Jun 1998 21:58:14 -0400 (EDT)
From: "David E. Brooks Jr" <dbj@iglou.com>
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To: Terry Lambert <tlambert@primenet.com>
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Subject: Re: mlock()/mclear (was Re: Unsupport calls)
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On Tue, 30 Jun 1998, David E. Brooks Jr wrote:

[ This is in regards to implementing mlock()/mclear() ]
> I haven't gotten very far (I'm re-reading relevant portions of _The
> Design and Implementation of 4.4 BSD Operating System_ and lots of
> stuff in section 9 right now), but I do have one question right off
> the bat.  Both mmap(2) and the newvm paper make mention of the
> MAP_HASSEMAPHORE flag; Why is (or was) this necessary?  All that comes
> to mind is multi-processor systems and keeping any copies of that
> page of memory synchronized.

Hmm, I think I can answer my own question: Mmap() needs to know since
any reference counts (for those waiting to lock) to a semaphore
structure have to be decremented properly when/if a page containing a
semaphore is munmap()-ed from memory (either explicitly or through
process termination).

-- Dave
(Who is now only beginning to realize why nobody has whipped this out
before...)

--
David E. Brooks Jr
  dbj@iglou.com


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