Mailinglist Archive: opensuse (794 mails)

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Re: [opensuse] Swap or paging? They are very very differnt?
  • From: "Carlos E. R." <robin.listas@xxxxxxxxxxxxxx>
  • Date: Thu, 30 Nov 2017 22:49:46 +0100 (CET)
  • Message-id: <alpine.LSU.2.21.1711302244130.14421@Telcontar.valinor>
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On Thursday, 2017-11-30 at 11:29 -0500, Anton Aylward wrote:
On 30/11/17 05:00 AM, Wols Lists wrote:


See Anton's definition of swapping - the COMPLETE process gets dumped to
disk.

As I understand paging, PART of a process gets pushed aside to make room.

What DIFFERENCE it makes, I have no idea, but the underlying techniques
are fundamentally different.

It makes a fantastic difference in the demands it paces on the hardware.

Paging, which is actually short for 'demand paging' means you can pull many
tricks with performance, but, as with everything, it is a compromise.

This starts with the memory being accessed being 'not there'.
Well, actually the mapping says that the referenced page hasn't been loaded.
So you get a fault.
The OS has to go off an get the relevant page of the code (or data) from disk
and while it is doing so that process is suspended and another one can run.

BUT, and this is the big issue, there needs to be the hardware capability to
restart the instruction that caused the fault.

Another issue was about needing to continue code that was "paged out", and thus it would deadlock.


THAT is non trivial.
It is also a capability the PDP-11 didn't have.
So the PDP-11 UNIX worked as 'rill in/roll out of the whole process.

Ah. But the 80386 processor did. I don't know about the 286, I think not.


- -- Cheers,
Carlos E. R.
(from openSUSE 42.2 x86_64 "Malachite" at Telcontar)

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