🚀 go-pugleaf

In article <960022@hpcljms.HP.COM> brians@hpcljms.HP.COM (Brian
Sullivan) writes:

| > Have read(2) and write(2) calls map the pages containing the buffers
| > out of the user address space and return immediately.  Once the
| > data have been copied (DMAed?) to/from the buffers, map the pages back in.
| 
|   Well,  I suspect that this solution will not work with most C programs.
| Why, because most of the time read(2) and write(2) are called with a
| buffer that is an auto-variable or stack allocated.  Telling the MMU to
| unmap a page in the users stack will have very dire consequences.  Maybe
| a better idea would be a new memory allocation, combined with new read(2)
| and write(2) calls.  Using this method the need to copy the users data
| would be solved.

What are you talking about?  How is unmapping a page because of an I/O
request (with an intent to map it back in when the I/O completes and
having page faults wait for the I/O completion) any different from any
normal time the OS unmaps a page to reuse the memory for something
else.  That is not a dire consequence, that is how virtual memory
works.
--
Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA, 02142

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