Date: Thu, 4 Dec 2008 17:11:46 -0500 From: "Josh Carroll" <josh.carroll@gmail.com> To: "Steve Polyack" <korvus@comcast.net> Cc: Alexandr Pakhomov <pahom.rt@gmail.com>, Mike Tancsa <freebsd-stable@freebsd.org> Subject: Re: repeatable crash on RELENG7 Message-ID: <8cb6106e0812041411t13ca9ffcjc4cc66a33ef43133@mail.gmail.com> In-Reply-To: <49384863.9040807@comcast.net> References: <20081204204803.EB8D34500F@ptavv.es.net> <49384863.9040807@comcast.net>
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> It seems that the term "swap-backed" is misleading for some people. It does > NOT mean your md(4) device will be constantly swapping to disk (and the man > page does an alright job of relaying this). It simply means that generally > available memory will be used, and so will swap iff available memory happens > to drop low enough. > > The bottom line in my experience with md(4) devices greater than ~100MB is > that "swap-backed" is always reliable, while malloc'd md(4) devices will > cause unpredictable kernel panics. Using -t swap instead of -t malloc will prevent a panic, but creating an md greater than the size of the VM available and filling it will cause resource exhaustion and OOM will kick in and start killing processes, right? So while it won't panic the box, I still wouldn't consider it safe to use unless the size of the md is chosen carefully. Someone please correct me if I'm wrong, but I think that'd be the behavior if an md with -t swap is used, right? Regards, Josh
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