Date: Wed, 8 Nov 2000 17:57:04 -0500 From: Keith Stevenson <keith.stevenson@louisville.edu> To: Terry Lambert <tlambert@primenet.com> Cc: "Daniel C. Sobral" <dcs@newsguy.com>, arch@FreeBSD.ORG Subject: AIX SIGDANGER (was Re: softdep panic due to blocked malloc) Message-ID: <20001108175704.B1405@osaka.louisville.edu> In-Reply-To: <200011081817.LAA21138@usr08.primenet.com>; from tlambert@primenet.com on Wed, Nov 08, 2000 at 06:17:14PM %2B0000 References: <3A09346F.7543C1DD@newsguy.com> <200011081817.LAA21138@usr08.primenet.com>
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This is a bit offtopic, but I couldn't help myself. (I'm an AIX admin) Quoting IBM's July 2000 system documentation CDROM: The system monitors the number of free paging space blocks and detects when a paging-space shortage exists. When the number of free paging-space blocks falls below a threshold known as the paging-space warning level, the system informs all processes (except kprocs) of this condition by sending the SIGDANGER signal. If the shortage continues and falls below a second threshold known as the paging-space kill level, the system sends the SIGKILL signal to processes that are the major users of paging space and that do not have a signal handler for the SIGDANGER signal (the default action for the SIGDANGER signal is to ignore the signal). The system continues sending SIGKILL signals until the number of free paging-space blocks is above the paging-space kill level. So, SIGDANGER doesn't buy you much unless your applications have a handler for it. (In my experience, most don't.) I was not very happy when I hit a low memory situation and AIX started committing random acts of violence against my process table. The system ended up being so hosed, I had to reboot to maintenance mode and repair a bunch of datafiles. (One of our production applications doesn't SIGKILL gracefully.) I think that SIGDANGER would make a lot more sense if its default action was the same as SIGTERM. SIGKILL'ing everything in sight isn't a lot cleaner (IMO) than letting the system crash. Regards, --Keith Stevenson-- -- Keith Stevenson System Programmer - Data Center Services - University of Louisville keith.stevenson@louisville.edu GPG key fingerprint = 332D 97F0 6321 F00F 8EE7 2D44 00D8 F384 75BB 89AE On Wed, Nov 08, 2000 at 06:17:14PM +0000, Terry Lambert wrote: > > > I haven't seen an occurrance of one in nature (well, AIX) in at > > > least 5 years. > > > > I did... :-( > > And wished the damned application knew about the signal and stopped > > hogging memory. > > ??? > > It's my experience that if you don't trap the thing, you > terminate. Did your application ignore the thing when you > didn't want it to, or did it terminate, when you didn't want > want it to? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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