swap byte size?!

[kalin mintchev]

thank you for the explanation. it helps...


> On 20:48 20 Jul 2004, kalin mintchev <kalin at el.net> wrote:
> | i want to add a swap file to my system. following the rule of 2 to 1 the
> | file would need to be 2 gigs because the ram is a gig. but using the dd
> | command what do i put for bs and count?
> | i was looking around on google but couldn't exactly find it..
>
> block size * count should equal your swap file size.
> You want count to be "small". So:
>
> 	% dc
> 	1024 1024 *p
> 	1048576
> 	% dd if=/dev/zero count=1024 bs=1048576 of=your-swap-file
> 	%
>
> In fact, you can probably do it in a single write:
>
> 	% dc
> 	1024 1024 1024 **p
> 	1073741824
> 	% dd if=/dev/zero count=1 bs=1073741824 of=your-swap=-file
>
> I just did that on a machine here and it took quite a while.  That may
> be because a big block size will map a chunk of memory, virtually,
> and as you fill it from /dev/zero that will cycle your RAM to swap as
> things fill. So probably you want a big blocksize, but not as big as
> possible. One megabyte should do nicely - big enough to move a lot of
> data per write, small enough that its memory footprint doesn't blow your
> RAM usage.
>
> The basic deal is that small block size and large count means lots of
> write() calls, and that is inefficiency because each such call has some
> overhead; to minimise that you minimise count and maximise blocksize
> without getting silly.
>
> Cheers,
> --
> Cameron Simpson <cs at zip.com.au> DoD#743
> http://www.cskk.ezoshosting.com/cs/
>
> The problem is, every time something goes wrong, the paperwork is found
> in order...     - Walker on NASA
>
>
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