Max size of one swap slice

Chuck Swiger cswiger at mac.com
Tue Aug 5 17:01:39 UTC 2008


On Aug 5, 2008, at 8:39 AM, Lin Jui-Nan Eric wrote:
> Recently we found that we can only allocate 32GB for one swap slice.
> Does there is any sysctl oid or any kernel option to increase it?  Why
> we have this restriction?

This size limitation likely predates the availability of disks larger  
than 32GB.

It's hard to conceive of why you'd want to add so much swap space,  
anyway-- if you've got programs which actually need to deal with 10s  
of gigabytes worth of data, then they ought to maintain a smaller/ 
reasonable-sized working set in RAM and do disk I/O as needed  
themselves rather than depend upon the VM pager, anyways.

(Well, when using a BSD-derived kernel, anyways.  Some of the Mach  
kernels support userland VM pager implementations, so that things like  
a database or Photoshop can provide their own pager which understands  
their workload and chooses which pages to evict or replace better than  
the default system pager algorithm can.)

Regards,
-- 
-Chuck



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