> What I've been told in the past (albeit on Red Hat, but that shouldn't > matter much) is, that with a 2.4.x kernel you do indeed need 2xRAM due > to the way 2.4 allocates memory. Under 2.2.x, I happily used swap just > up to the amount of total memory I envisaged to be necessary. > Unfortunately, I'm not a kernel expert, so I don't know the exact > reasoning behind this advice for 2.4.x.
Up to about kernel 2.4.10, swap required at least the size of RAM to be additional. In other words, if you had 128M or RAM and 384M of SWAP, you'd only have 384M working memory, not 512M. This changed after about 2.4.10 so all swap was additive, which was similar behaviour to 2.2 kernels. I think that the 2X rule of thumb originated in days when 8M to 32M of memory was common, so allocating 64M or 128M was workable. With the average machine having 512M to a gig of physical RAM this doesn't seem to make as much sense. I've written before that 1G of swap space on today's large hard drives is relatively smaller than 128M on older drives; in that light having large swap space doesn't seem so unusual. On the other end of the spectrum you can run entirely without swap by using memory overcommit and many people are happy doing so. -- The Digital Hermit Unix and Linux Solutions http://www.digitalhermit.com [EMAIL PROTECTED]
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