Re: VM object cache misses
Re: VM object cache misses
- Subject: Re: VM object cache misses
- From: Godfrey van der Linden <email@hidden>
- Date: Fri, 15 Jan 2010 17:55:20 +1100
On 2010-01-15, at 3:16 PM, Godfrey van der Linden wrote: G'day, All.
I was captured while passing a friend today and asked a question I couldn't answer. What is the "Object cache" reported by vm_stat and why is its hit-rate so low?
This is a vm_stat report from my 10.6.2 '06 iMac.
Mach Virtual Memory Statistics: (page size of 4096 bytes) Pages free: 52226. Pages active: 221914. Pages inactive: 40479. Pages speculative: 7129. Pages wired down: 71206. "Translation faults": 374933705. Pages copy-on-write: 3220998. Pages zero filled: 228364806. Pages reactivated: 45183. Pageins: 417732. Pageouts: 32436. Object cache: 193 hits of 1728118 lookups (0% hit rate)
Further here is the uptime on my system
14:50 up 11 days, 5:34, 10 users, load averages: 0.38 0.22 0.17
In a system that has been up 11 days only 193 hits from 2 million attempts seems to indicate that the cache is pointless. This cache only seems to get hit on average twice a second.
Godfrey
What I meant was cache lookup only occurs on average twice a second, and the hit rate is only every hour and a half on average.
Seems like a false optimisation
Godfrey
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