Messages in this thread | | | From | "Timothy Miller" <> | Subject | Page compression in lieu of swap? | Date | Sat, 12 Apr 2003 18:35:19 -0400 |
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I did some searching of the kernel archives and the only things related to the forthcoming idea had to do with compressing pages when writing to swap and doing compressed disks. Here's a different idea...
Inspired by my recent experiments in compressing kernel messages, I started to wonder what else might benefit from compression, and the following idea occurred to me:
Given the hideous amount of time required to access a disk, especially when something else wants to access it, could there be a benefit to "swapping" pages by compressing them to somewhere else in memory? If we could achieve, even say, 30% compression on pages, on average, then we could free up RAM without having to do any I/O. This would be the first line of defense against a low-memory situation, finally resorting to actual disk access when that becomes unworkable or for pages which can't be compressed enough for it to help (which has a penalty worse than just writing to disk). And furthermore, if we were to swap first memory containing compressed pages, we can reduce the total amount of I/O for swapping.
This would, of course, suck a lot of CPU, and in the case of a server running many services where the CPU usage is pegged even when there's a lot of swapping, it would be better to just swap as normal. But in any case where swapping is causing an increase in idle time, I would expect a considerable benefit from being able to free up pages by making LRU pages simply take up less space in RAM when they're not being used.
Comments?
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