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Date:      Mon, 6 Sep 2010 14:04:06 +0300
From:      Kostik Belousov <kostikbel@gmail.com>
To:        Andriy Gapon <avg@icyb.net.ua>
Cc:        freebsd-fs@freebsd.org, jhell <jhell@DataIX.net>
Subject:   Re: zfs very poor performance compared to ufs due to lack of cache?
Message-ID:  <20100906110406.GC2396@deviant.kiev.zoral.com.ua>
In-Reply-To: <4C84C857.1070306@icyb.net.ua>
References:  <7EA7AD058C0143B2BF2471CC121C1687@multiplay.co.uk> <1F64110BFBD5468B8B26879A9D8C94EF@multiplay.co.uk> <4C83A214.1080204@DataIX.net> <06B9D23F202D4DB88D69B7C4507986B7@multiplay.co.uk> <4C842905.2080602@DataIX.net> <330B5DB2215F43899ABAEC2CF71C2EE0@multiplay.co.uk> <4C84C857.1070306@icyb.net.ua>

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On Mon, Sep 06, 2010 at 01:54:15PM +0300, Andriy Gapon wrote:
> on 06/09/2010 02:57 Steven Hartland said the following:
> > Based on Jeremy's comments I'm updating the box the stable. Its buildin=
g now
> > but will be the morning before I can reboot to activate changes as I ne=
ed to
> > deactivate the stream instance and wait for all active connections to f=
inish.
> >=20
> > That said the problem doesn't seem to be cache + free but more cache + =
free
> > + inactive with inactive being the large chunk, so not sure this change
> > would make any difference?
> >=20
> > How does ufs deal with this, does it take inactive into account? Seems =
a bit
> > silly for inactive pages to prevent reuse for extended periods when the
> > memory could be better used as cache.
>=20
> Inactive pages are also a cache, just a different kind.
Not quite. Inactive pages may be dirty. Such pages cannot be freed or reused
without pageout.

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