Thus spake Peter Wemm <[EMAIL PROTECTED]>: > One system I used to use years and years ago seperated this process into > stages. The swap(1M) command could be used to enable, disable and 'weight' > allocation to swap areas. The add was easy. 'delete' would cause the > device to be attempted to be paged in, but if the system looked like it was > going to run out of resources it would fail and stop right there. You could > either turn allocation back on, or kill processes or wait for the pager catch > up with moving stuff out to other swap spaces. When (if) it finally hit > zero inuse, it would be deleted. > > It did manage multiple swap spaces as seperate entities with different fill > levels etc [rather than one giant logical swap area], so doing it this way > kinda made sense. I did actually use it once and it even worked. :-) > (I cannibalized my /tmp file system and used it for swap for a project, and > then turned it off and re-mkfs'ed it)
The weight idea is very interesting. NetBSD does this using priorities; all the swap devices of a given priority are filled round robin before devices of lower priority, the idea being that the slower ones are a last resort (e.g. NFS). On the other hand, this design allows large and fast swap devices to start swapping to death before the `backup' devices see any action. It isn't clear to me whether priorities or "fill levels" are better. (Certainly a hybrid is possible, that is, weights within priority levels.) This may be a better project for me than swapoff in the immediate future because I won't have to understand how to track down the appropriate VM objects and handle them in a kosher manner. Implementing weights/priorities will also involve dynamically allocating struct swdevt's, which should be done anyway and will only be harder after swapoff() is written. BTW, I believe the comment about swfree() in vm_swap.c is outdated as of rev. 1.17, and nothing uses SW_FREED anymore. This means that technically, swap devices don't have any flags right now, but that could change with swapoff(). To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
