Am 20.08.17 um 01:39 schrieb Greg 'groggy' Lehey: >> 3. should total swap be 1x 2x or some other multiple of RAM these days? > > It never needed to be. The only issue is that if you want processor > dumps, you once needed a swap partition (and not a swap file) at least > marginally larger than memory. With compressed dumps, that > requirement is relaxed, but I suspect that a 4 GB partition could be > too small.
Well, no, it (2x RAM) used to be needed at a time ... ;-) The VAX supported paging, but did not use a multi-level page table as most CPUs do today. There was a linear list of page addresses per process, and new page allocations could lead to a situation, where there was no free space in this list. This required a kind of garbage collection run, which was implemented by swapping out all processes and starting with a clean state. This required 2 times RAM configured as swap, to prevent a dead-lock (when a new page needed to be allocated to complete the swap-out). This MMU was used in at least all VAX 11-7xx, the µVAX 2 and µVAX 3 and thus in many of the machines used to run BSD back in the 80s ... And thus, swap of at least 2 times RAM used to be not just a best practice, but a strict requirement for stable operation of these machines. Regards, STefan _______________________________________________ freebsd-current@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
