Date: Tue, 22 Jan 2019 08:46:51 +0100 From: Andrea Venturoli <ml@netfence.it> To: "Kevin P. Neal" <kpn@neutralgood.org> Cc: freebsd-questions@freebsd.org Subject: Re: The mysterious kern.maxswzone Message-ID: <6556ab0d-d250-b418-6704-2b32c8b3cf08@netfence.it> In-Reply-To: <20190121204421.GA20854@neutralgood.org> References: <20190116022046.GA45024@admin.sibptus.ru> <50f1f8d5-7db6-4abb-6beb-c82f17396304@netfence.it> <20190121204421.GA20854@neutralgood.org>
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On 1/21/19 9:44 PM, Kevin P. Neal wrote: > With the difference in performance between a CPU and disk, does relying > on swap space make sense anymore? I think it still does. Of course performance will be terrible, but it can be acceptable for short periods of time: e.g. I've got a box which will swap considerably when periodic is run, but that happens at night and no one will notice. Also, I prefer an occasional slow down to processes being occasionally killed. If the machine constantly and heavily swapping, it's time for either a software diet or hardware upgrade. > The x1 and x2 rules of thumb come from a different era. One thing to keep in mind are crash dumps: they are written in a swap partition, so, if you don't have enough and your box panics, you won't be able to debug it. I've been hit in the past by this: a box's swap was be taylored to RAM size, the RAM was doubled and crash dump could not be obtained anymore. I also heard something about "minidumps", or compressed dumps, but did not investigate... so yes, all this *might* be obsolete; however, with modern HD sizes (1TB at the least) I prefer to "waste" some more space for swap, than to be sorry later. That's also why I don't bother about kern.maxswzone: I have some swap space I don't need *now*; it's just sitting there for eventual future needs :) > Oh, and won't swapping to a GEOM mirror cause deadlocks? I thought so, but > I wouldn't take my word for it. I have several boxes with swap on GMIRRORs and I've never seen any deadlock due to this fact. Just my experience... perhaps there are corner cases? bye av.
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