Date: Mon, 24 Mar 2003 23:53:29 -0500 From: Garance A Drosihn <drosih@rpi.edu> To: Wes Peters <wes@softweyr.com>, John Baldwin <jhb@FreeBSD.ORG> Cc: freebsd-arch@FreeBSD.ORG Subject: Re: Patch to protect process from pageout killing Message-ID: <p05200f43baa58a1eb364@[128.113.24.47]> In-Reply-To: <200303241752.40245.wes@softweyr.com> References: <XFMail.20030324140902.jhb@FreeBSD.org> <200303241752.40245.wes@softweyr.com>
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At 5:52 PM -0800 3/24/03, Wes Peters wrote:
>On Monday 24 March 2003 11:09, John Baldwin wrote:
> > I think that adopting the SIGDANGER approach would be better
> > rather than rolling our own private interface.
>
>It's not clear to me the SIGDANGER interface allows me to say
>"go elsewhere bub, I'm really important." In this case, that
>is essential. I think even in the general FreeBSD case you can
>make a point for a setting like this in, say, named.
Please check out the descriptions I posted previously. SIGDANGER
(as implemented by AIX) explicitly provides two things. The process
gets to decide which one they (the process) wants:
1) signal me at the first sign of trouble, and I'll free
up some virtual memory (possibly by exit()-ing).
2) do not ever kill me to free up memory.
I think that we could improve upon the AIX implementation if we
wanted to, but I think people are so used to having problems with
AIX that they hate the idea of SIGDANGER as soon as they see the
letters AIX. Having used AIX for more than ten years now, I can
sympathize with that, but in the specific case of SIGDANGER there
is an idea that can work quite well.
(reference on sigdanger was at:
http://nscp.upenn.edu/aix4.3html/aixbman/baseadmn/pag_space_under.htm
)
>The SIGDANGER interface worries me in general, partly because it's
>a signal and partly because it complicates the design of EVERYTHING
>just to handle it. I guess a lot depends on the implementation
>details of how SIGDANGER and the default handlers are designed,
>but nothing I saw last week gave me a warm fuzzy about that.
I don't know enough about the lower-level implementation details,
but I did think the recent discussion on the src-committers list
did include a number of good ideas. I am horribly over-committed
with things that I've promised to do (including stuff for my real-
world job...), so I can't look into SIGDANGER ideas right now, but
I'm more than happy to try to explain how it should work.
--
Garance Alistair Drosehn = gad@gilead.netel.rpi.edu
Senior Systems Programmer or gad@freebsd.org
Rensselaer Polytechnic Institute or drosih@rpi.edu
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