[X4U] Having Windows open drain resources?

[David Ledger]

At 12:43 -0500 7/4/09, Ed Gould wrote:
>On Apr 7, 2009, at 5:43 AM, David Ledger wrote:
>>  At 18:41 -0500 5/4/09, Ed Gould wrote:
>>>  This is a general questions for all operating systems. It really 
>>>depends on the OS (for VM) . There is not hard and fast answer as 
>>>(IIRC) it depends on how the OS "polls" (looks to see if there is 
>>>something to do) AND how the VM handles paging. IIRC the VM for 
>>>PC's is immature and not great for paging where as other OS's semi 
>>>talk to VM and let VM carry out the paging . Since the VM 
>>>version(for PC's) is not sophisticated  I would suspect that there 
>>>is essentially double page ins and the same for pageouts(this is 
>>>only a guess).
>>>  Bottom line it depends on the OS.
>>  The VM PCs use isn't really relevant. The way VM is done on Unix 
>>is fairly well known at different time frames. What OS X uses may 
>>not be a sophisticated as in HP-UX (say), but not far off.

>I disagree. Double paging is bad and especially in small computer 
>land as I/O is sooooo slow and the inability to chain I/O requests 
>(so that say 20 I/O operations get done but with only one trip 
>thought the code to do I/O). I have worked on systems that do a 
>"handshake" between the OS and VM so VM does the paging it is a 
>really nice and time saving feature. Some OS's know that they are 
>running under VM and do this automatically others you have to tell 
>them (each OS does it slightly differently).

Do you have any evidence that OS X does "Double paging" (please 
define this). Admittedly the I/O will slow paging down on a Mac 
compared to on a system costing 10 to 1000 times as much, but I've no 
reason to suspect that the VM system in OS X is significantly 
different to that in Unix machines in that higher cost class.

You keep referring to machines / OS that you have worked on in the 
past, but never say what the OS is. Please tell us, or we might just 
think that it's so old that its special features are standard now :-).

I've used so many OSs over the years that I've lost count, but since 
'83 it's been mainly Unix flavours. And OS X is a Unix flavour.

David


-- 
David Ledger - Freelance Unix Sysadmin in the UK.
HP-UX specialist of hpUG technical user group (www.hpug.org.uk)
david.ledger at ivdcs.co.uk
www.ivdcs.co.uk