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Date:      Sun, 30 Sep 2001 23:41:14 -0500
From:      Alfred Perlstein <bright@mu.org>
To:        Greg Lehey <grog@FreeBSD.org>
Cc:        Jos Backus <josb@cncdsl.com>, hackers@FreeBSD.ORG
Subject:   Re: VM: dynamic swap remapping (patch)
Message-ID:  <20010930234114.P59854@elvis.mu.org>
In-Reply-To: <20011001131951.M31215@wantadilla.lemis.com>; from grog@FreeBSD.org on Mon, Oct 01, 2001 at 01:19:51PM %2B0930
References:  <20010929232953.B341@eix.do-labs.spb.ru> <20010929175653.Z59854@elvis.mu.org> <20010930120328.A534@eix.do-labs.spb.ru> <20010930035529.G59854@elvis.mu.org> <20010930134437.B284@eix.do-labs.spb.ru> <20010930105509.B2220@lizzy.bugworks.com> <20010930142326.L59854@elvis.mu.org> <20010930123359.A7241@lizzy.bugworks.com> <20010930145558.M59854@elvis.mu.org> <20011001131951.M31215@wantadilla.lemis.com>

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* Greg Lehey <grog@FreeBSD.org> [010930 22:49] wrote:
> On Sunday, 30 September 2001 at 14:55:58 -0500, Alfred Perlstein wrote:
> > * Jos Backus <josb@cncdsl.com> [010930 14:35] wrote:
> >> On Sun, Sep 30, 2001 at 02:23:26PM -0500, Alfred Perlstein wrote:
> >>> * Jos Backus <josb@cncdsl.com> [010930 12:55] wrote:
> >>>> AIX has SIGDANGER.
> >>>
> >>> Anyone care to tell me how it works in AIX?  If the interface is
> >>> nice, cloning it would be kind of cool.
> >>
> >> I don't currently have access to an AIX system, but
> >>
> >> http://as400bks.rochester.ibm.com/doc_link/en_US/a_doc_lib/aixbman/admnconc/pag_space_under.htm
> >>
> >> has some (useful) info.
> >
> > It sure does!
> >
> > I think I'm going to make a proposal on -arch about this, to be
> > perfectly honest, AIX has a good implementation, I haven't read it
> > all yet, but it doesn't look like it gives the applications a
> > notification when the danger is gone, we'll have to figure that out,
> > or I'll have to read more into this.
> 
> If it's any help, I have an AIX box here.  It belongs to IBM, so I
> have to respect security issues, but I'll do what I can.

Well Joe seems to have provided a pretty interesting document on
how it works in AIX, but I was wondering if they do anything wrt
low/high watermarks like my idea.

Basically you'd like to inform processes that the danger has been
alliviated so that they can cautiously start accepting more work
rather than freaking out and shutting out clients forever...

This might lead to a situation where SIGDANGER starts getting
sent informing that things are looking bleak, then processes
start freeing resources, they get the second SIGDANGER to let
them know that things are looking ok so they ramp up again and
the cycle repeats, I guess that's not optimal, but I'd like FreeBSD
to let processes know that things are looking better so they can
go from "scrooge mode" to "thrifty mode".

-- 
-Alfred Perlstein [alfred@freebsd.org]
'Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.'

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