Max size of one swap slice

Max Laier max at
Tue Aug 5 17:19:36 UTC 2008

On Tuesday 05 August 2008 17:39:11 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 is a consequence of the data structure used to manage swap space.  See 
sys/blist.h for details.  It *seems* that you *might* be able to increase the 
coverage by decreasing BLIST_META_RADIX, but that's from a quick glance and 
most certainly not a good idea.

However, the blist is a abstract enough API so that you can likely replace it 
with something that supports 64bit addresses (and thus 512*2^64 bytes of swap 
space per device) ... but I don't see why you'd want to do something like 
this.  Remember that you need memory to manage your swap space as well!

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