From mboxrd@z Thu Jan 1 00:00:00 1970 To: 9fans@cse.psu.edu Subject: Re: [9fans] Virtual memory in BSD and Plan9 From: "rob pike" MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Message-Id: <20011029123819.DCCD7199E4@mail.cse.psu.edu> Date: Mon, 29 Oct 2001 07:38:17 -0500 Topicbox-Message-UUID: 100137da-eaca-11e9-9e20-41e7f4b1d025 I'm a radical here, but I think if a machine is paging, you've lost. To me, VM is a pretty technique for memory management in the kernel, something distinct from paging, which is a way to get the system through temprorary overshoots in memory demand. My boss when the first Plan 9 kernel was being written was Sandy Fraser, who had worked on Atlas, one of the first VM systems. When he heard that I was putting VM into Plan 9 (a situation more accurately described as building Plan 9's original memory manager around a VM model), he literally called me on the carpet. He said that he hated VM bitterly because of the Atlas days, in which nothing got done because the system was always thrashing. I pointed out the distinction between VM and paging, explained that I was implementing VM but not paging (Phil W. put paging in a few years later), and justified my decision by pointing out that with memory so cheap today, there was really no reason to depend on the paging system to manage your working set except for the occasional brief overrun on demand. -rob