Hello,

MacOS X virtual memory seems really close (at least in appearence) to NeXT virtual memory (swapfiles stored in /private/...). But unfortunately, swaptab (man swaptab) looks like a no longer supported feature.
Due to the lack of MacOS X documentation, I'm not certain of what NeXT features are still active under MacOS X. I would like to put swapfiles on another faster HD, but I can't find how to do this.

I would also like creating a RAM disk. As I have a pretty confortable amount of RAM (448 Mo) I can easily spend 128 or 192 Mo for a RAM disk. Is it possible with MacOS X ?

And finaly (some of you have already guess) if above questions have a positive answer, is it possible to store swapfile ON the RAM disk ?

--- last news :

after further investigation, it appears that swaptab is used on MacOS XS, but not in MacOS X.
I've made a 'grep swap *' in the /etc/ directory. It pointed out that in MacOS X the file rc is handling swap init. So I've edited the rc file by replacing :

swapdir=/private/var/vm

by

swapdir=/scratch/vm

where 'scratch' is an empty partition of my second IDE HD. (with an empty folder 'vm' at its root)

Unfortunately, next reboot created a folder called 'scratch' at '/' and mounted the volume 'scratch' as 'scratch 1'. It's quite strange because in rc file, mount seems to occur before swap init....

So, for now, I can put swap file where I want to... but only on the boot disk : absolutely not interesting.

I wonder what this could lead to :

swapdir=/dev/disk2s11/vm # it's the device mounted on 'scratch'

total anihilation of my system or hack on the day ? As /dev/disk2s11 is not a folder, I'll bet on anihilation, but who knows...

[This message has been edited by patpro (edited 12-10-2000).]

[hidozage]

what I really wanted to do under Mac OS X PB is turn off swap. any ideas?

[Scott_H]

Due to the techy nature of this I'm going to move this over to the Mac OS X Support forum. Click through to find your post.

[zpincus]

Turning off swap or offloading it to a ramdisk (same thing, essentially, but the former is a bit more clean) really isn't a good idea.

VM made previous versions of the Mac OS really sluggish. But the *NIX idea of swap, especially as implemented in BSD, is a very high performance system that doesn't slow anything down until you've actually maxed out the RAM. Then (AFAIK) the disk is used to page infrequently used mem areas to reclaim the space for more frequent uses. It makes your system use the RAM it has a lot more efficiently. Apple's old implementation had a lot of paging problems, used a lot of disk space, and, basically sucked. *NIX-style paging is more like how RamDoubler ran (minus the compression) but a lot more mature and geared 100% for performance.


Don't believe me? The major servers here on campus that run Solaris, our IRIX graphicks workstations, et. al. all have about 3x (at least) swap as RAM. The swap boosts performance on heavily loaded systems (insofar as being able to do more with only a minimal hit in speed is better than not being able to do more). Every major corporate server out there uses swap to make its RAM use more efficient under loaded circumstances. This alone should convince you that it isn't a performance drain likethe VM of OS 9 and below.

Also, in a multiuser system where you have a lot of daemons logged in that usually aren't doing a whole lot (sshd, ftpd, apache, to name a few), it is REALLY HELPFUL to be able to page these fellows to disk and use "their" RAM for current apps, and only have them using system RAM when active (serving pages, or files, and the like. Since I don't run a really actice web page, its nice to not have the apache system in real RAM all the time.)

Does that help?

Zach

[zpincus]

Turning off swap or offloading it to a ramdisk (same thing, essentially, but the former is a bit more clean) really isn't a good idea.

VM made previous versions of the Mac OS really sluggish. But the *NIX idea of swap, especially as implemented in BSD, is a very high performance system that doesn't slow anything down until you've actually maxed out the RAM. Then (AFAIK) the disk is used to page infrequently used mem areas to reclaim the space for more frequent uses. It makes your system use the RAM it has a lot more efficiently. Apple's old implementation had a lot of paging problems, used a lot of disk space, and, basically sucked. *NIX-style paging is more like how RamDoubler ran (minus the compression) but a lot more mature and geared 100% for performance.


Don't believe me? The major servers here on campus that run Solaris, our IRIX graphicks workstations, et. al. all have about 3x (at least) swap as RAM. The swap boosts performance on heavily loaded systems (insofar as being able to do more with only a minimal hit in speed is better than not being able to do more). Every major corporate server out there uses swap to make its RAM use more efficient under loaded circumstances. This alone should convince you that it isn't a performance drain likethe VM of OS 9 and below.

Also, in a multiuser system where you have a lot of daemons logged in that usually aren't doing a whole lot (sshd, ftpd, apache, to name a few), it is REALLY HELPFUL to be able to page these fellows to disk and use "their" RAM for current apps, and only have them using system RAM when active (serving pages, or files, and the like. Since I don't run a really actice web page, its nice to not have the apache system in real RAM all the time.)

Does that help?

Zach