Very Large "zero" slab expected?

Sonny Rao sonny at
Wed Feb 2 06:52:07 EST 2005

Hi, I'm running a fairly heavy database workload using DB/2 on a 4-way
720 ontop of ext3 trying to replicate a separate VM performance issue.

During and after the run, I see a massive about of slab memory being
used by the "zero" cache, which appears to a be a ppc64 specific
cache for pmd's and pgd's.  

Basically, about 1GB out of my total of 8GB on the system is being
consumed by this.  Is this expected ?  It seems excessive
considering my mapped memory is only about 2GB during the run.

The DB/2 buffer pool was set to 4GB and none of it used hugh pages.

Here's the relavent snippet from slabinfo:
slabinfo - version: 2.0
# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <batchcount> <limit> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
zero              256424 256431   4096    1    1 : tunables   24   12 8 : slabdata 256424 256431      0

Any ideas as to why there are so many of these ?


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