Re: Improvement on memory subsystem

From: Ian Stirling
Date: Wed Jul 19 2006 - 05:17:52 EST

Valdis.Kletnieks@xxxxxx wrote:
On Tue, 18 Jul 2006 18:03:54 +0800, yunfeng zhang said:

2. Read-ahead process during page-in/out (page fault or swap out) should be
based on its VMA to enhance IO efficiency instead of the relative physical pages
in swap space.

But wouldn't that end up causing a seek storm, rather than handling the pages
in the order that minimizes the total seek distance, no matter where they are
in memory? Remember - if you have a 2Ghz processor, and a disk that seeks in 1
millisecond, every seek is (*very* roughly) about 2 million instructions. So
if we can burn 20 thousand instructions finding a read order that eliminates
*one* seek, we're 1.98M instructions ahead.

To paraphrase shakespear - all the world is not a P4 - and all the swap devices are not hard disks.

For example - I've got a 486/33 laptop with 12M RAM that I sometimes use , with swapping to a 128M PCMCIA RAM card that I got from somewhere.

20K instructions wasted on a device with no seek time is just annoying.

And on my main laptop - I have experimented with swap-over-wifi to a large ramdisk on my server - which works quite well. (until the wifi connection falls over).
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