Re: dynamic allocation of swap disk space

[Ray Bryant <raybry@sgi.com>]

Silviu Marin-Caea wrote:
>
> 
> My desktop has been thrashing the disk for a couple of hours because
> the swap space was exhausted.  And I have the ambition to leave it alone
> to see if it ever comes out of the thrashing.  Of course, it's not usable
> at all during this time, I'm writing this on the laptop.
> 
>

You've got a couple problems mixed together here.

(1)  Swap space fills up because you have overcommitted memory.  In principle, 
filling up swap space has nothing to do with "thrashing".
(2)  "thrashing" is a characteristic of a poorly performing program in a
demand paging virtual memory system typically caused by trying to run a 
program with a resident size that is smaller than required.  Systems can 
thrash without filling up swap space.  It is true that systems can thrash AND 
fill up swap space, but it is not always so.

You either need (1)  more main memory, (2) reduce the number of programs you 
are running simultaneously, or (3) better behaving programs, or all three. 
Increasing the amount of swap space will just use more disk.  It won't cause 
your system to stop thrashing since that is driven by what is going on in 
memory, not what is going on on the disk.

Anyway, if swap space is full, then main memory is (nearly) full, and this is 
not a good time to do major surgery to your file system (e. g. increase the 
size of the swap space).  You may not be able to allocate the required memory 
to complete that job and then your system will crash.
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