Stephen Harris wrote:
In older BSD systems (eg around SunOS 4 times or before) swap space was
utilised oddly; all memory was allocated from swap, so you needed _at
least_ <physmem> of swap just to use all your real memory!  So if you
added <physmem> of swap then your total virtual memory size was still
only <physmem>.  No help!  So the rule of thumb came along that said
"swap = 2*<physmem>" and that gave you a VM of 2*<physmem>.


<old codger hat> this was also how early IBM System/370 DOS/VS worked... the swap space (which was contiguous cylinders of the disk, btw) was mapped 1:1 to virtual memory address space </old codger hat>

now, on late model Solaris, 'swap' is also used as tmpfs, which /tmp and /var/run utilizes by default, so you definitely want to allocate sufficient swap space for this at least, regardless of how large your physical memory is.


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