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Date: Sat, 18 Sep 2010 14:27:43 +0300
From: Andriy Gapon <avg@freebsd.org>
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To: Robert Watson <rwatson@freebsd.org>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: zfs + uma
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on 18/09/2010 14:23 Robert Watson said the following:
> I've been keeping a vague eye out for this over the last few years, and haven't
> spotted many problems in production machines I've inspected.  You can use the
> umastat tool in the tools tree to look at the distribution of memory over
> buckets (etc) in UMA manually.  It would be nice if it had some automated
> statistics on fragmentation however.  Short-lived fragmentation is likely, and
> isn't an issue, so what you want is a tool that monitors over time and reports
> on longer-lived fragmentation.
> 
> The main fragmentation issue we've had in the past has been due to mbuf+cluster
> caching, which prevented mbufs from being freed usefully in some cases.  Jeff's
> ongoing work on variable-sized mbufs would entirely eliminate that problem...

Robert,

just in case, this thread is not about fragmentation, it's about per-cpu
buckets, number of items in them and size of the items.

-- 
Andriy Gapon