ashley@cheops.eecs.unsw.oz (Ashley M. Aitken) (01/17/90)
G'Day,
I am interested in finding out more information about Mapped Segments and
Shared Memory on Apollo Domain Workstations (and the DN10000).
I am writing an application which consists of multiple processes which need
to share LARGE amounts of data (perhaps megabytes) and have access to this
data as fast as normal process memory (if this is possible).
At present I am looking into System V Shared Memory. This seems to be good
but I would like to know more about:
Shared Memory Limitations
How big can you make the shared memory segment on the Apollos, and
what sort of costs does one invoke if a large amount of shared memory
is used?
Most System V Shared Memory systems have a system constant called
something like SHMMAXPGS which states the maximum number of shared
memory pages globablly.
Where can I find this constant on the Apollos?
What are the implications of changing it?
What are the limits of its value?
Apollo presents some alternative(s) to Shared Memory through the use of Mapped
Segments etc. Mapped Segments associate part of the process address space with
a disk file, and swaps the relevant pages in when required. This seems to be
rather good too. Since even shared memory must be swapped out now and then,
but I would like to know more about:
Shared Memory vs Mapped Segments
How do Shared Memory and Mapped Segments compare for speed of use?
What are the restricition on Mapped Segments size and the costs this
may have on the system?
In general Mapped Segments would seem to be the nicer alternative because one
would always have a permanent copy of the data being shared. However SPEED IS
VERY IMPORTANT FOR THIS APPLICATION and if swapping in and out will reduce the
speed I will have to settle for Shared Memory or something else.
If anyone has any ideas, hints, experience or suggestions (of alternatives) I
would be most grateful if they could e-mail me at the address given below, I
will post a summary if there is a lot of interest.
Thanks in Advance,
Ashley Aitken.
E-MAIL ashley@cheops.eecs.unsw.oz ACSnet
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