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Date: Tue, 21 Sep 2010 10:09:28 +0300
From: Andriy Gapon <avg@freebsd.org>
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To: Jeff Roberson <jroberson@jroberson.net>
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Cc: Andre Oppermann <andre@freebsd.org>, Jeff Roberson <jeff@freebsd.org>,
	Robert Watson <rwatson@freebsd.org>, freebsd-hackers@freebsd.org
Subject: Re: zfs + uma
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on 21/09/2010 09:39 Jeff Roberson said the following:
> I'm afraid there is not enough context here for me to know what 'the same
> mechanism' is or what solaris does.  Can you elaborate?

This was in my first post:
[[[
There is this good book:
http://books.google.com/books?id=r_cecYD4AKkC&printsec=frontcover
Please see section 6.2.4.5 on page 225 and table 6-11 on page 226.
And also this code:
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/kmem.c#971
]]]

> I prefer not to take the weight of specific examples too heavily when
> considering the allocator as it must handle many cases and many types of
> systems.  I believe there are cases where you want large allocations to be
> handled by per-cpu caches, regardless of whether ZFS is one such case.  If ZFS
> does not need them, then it should simply allocate directly from the VM. 
> However, I don't want to introduce some maximum constraint unless it can be
> shown that adequate behavior is not generated from some more adaptable algorithm.

Yes, I agree in general.
But sometimes simplicity has its benefits too as opposed to complex dynamic
behavior that _might_ result from adaptive algorithms.

Anyway, I have some early patches to implement first two of your suggestions and
I am testing them now.  Looks good to me so far.
Parameters in the adaptions would probably need some additional tuning.

-- 
Andriy Gapon