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Date:      Wed, 26 Jan 2011 21:10:07 +0000
From:      "Robert N. M. Watson" <rwatson@freebsd.org>
To:        mdf@FreeBSD.org
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org
Subject:   Re: svn commit: r217830 - head/share/man/man9
Message-ID:  <161C86E9-A24C-4E71-90C6-26C3B47ACC1B@freebsd.org>
In-Reply-To: <AANLkTimn0te0NKR%2BusYC6CzxUVVaP%2BnpZKstsw1mWC7o@mail.gmail.com>
References:  <201101251739.p0PHdqKX044842@svn.freebsd.org> <alpine.BSF.2.00.1101260929430.44308@fledge.watson.org> <AANLkTimqyPYah5=yWHVxf3Us4=cBYKGkb0oyAE%2B7R-%2Bt@mail.gmail.com> <12EB1BEA-F0AF-4B2A-AFEB-9C38C7994FA8@freebsd.org> <AANLkTimn0te0NKR%2BusYC6CzxUVVaP%2BnpZKstsw1mWC7o@mail.gmail.com>

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On 26 Jan 2011, at 18:29, mdf@FreeBSD.org wrote:

>> I suppose an important question is now often we see this actually =
failing
>=20
> I don't believe we've ever seen a memory failure relating to sysctls
> at Isilon and we've been using the equivalent of this code for a few
> years.  Our machines aren't low memory but they are under memory
> pressure sometimes.

The kinds of cases I worry about are things like the tcp connection =
monitoring sysctls. Most systems have a dozen, hundred, or a thousand =
connections. Some have half a million or a million. If we switched to =
requiring wiring every page needed to store that list, it would do =
terrible things to the system. So really what I have in mind is: either =
we handle cases like that well, or we put in a clear warning and have =
obvious failure modes to catch the cases where it didn't work out. In =
practice, I think we would not want to switch the tcpcb/inpcb sysctl for =
this reason, but as people say "ah, this is convenient" we need to make =
sure it's handled well, and easy to debug problems when they do arise.

Robert=



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