[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [XEN] using shmfs for swapspace
hi, am starting to play with XEN - the virtualisation project (http://xen.sf.net). i'll give some background first of all and then the question - at the bottom - will make sense [when posting to lkml i often get questions asked that are answered by the background material i also provide... *sigh*] each virtual machine requires (typically) its own physical ram (a chunk of the host's real memory) and some virtual memory - swapspace. xen uses 32mb for its shm guest OS inter-communication. so, in the case i'm setting up, that's 5 virtual machines (only one of which can get away with having only 32mb of ram, the rest require 64mb) so that's five lots of 256mbyte swap files. the memory usage is the major concern: i only have 256mb of ram and you've probably by now added up that the above comes to 320mbytes. so i started looking at ways to minimise the memory usage. first, reducing each machine to only having 32mb of ram, and secondly, on the host, creating a MASSIVE swap file (1gbyte), making a MASSIVE shmfs/tmpfs partition (1gbyte) and then creating swap files in the tmpfs partition!!! the reasoning behind doing this is quite straightforward: by placing the swapfiles in a tmpfs, presumably then when one of the guest OSes requires some memory, then RAM on the host OS will be used until such time as the amount of RAM requested exceeds the host OSes physical memory, and then it will go into swap-space. this is presumed to be infinitely better than forcing the swapspace to be always on disk, especially with the guests only being allocated 32mbyte of physical RAM. here's the problems: 1) tmpfs doesn't support sparse files 2) files created in tmpfs don't support block devices (???) 3) as a workaround i have to create a swap partition in a 256mb file, (dd if=/dev/zero of=/mnt/swapfile bs=1M count=256 and do mkswap on it) then copy the ENTIRE file into the tmpfs-mounted partition. on every boot-up. per swapfile needed. eeeuw, yuk. so, my question is a strategic one: * in what other ways could the same results be achieved? in other words, what other ways can i publish block devices from the master OS (and they must be block devices for XEN guest OSes to be able to see them) that can be used as swap space, that will be in RAM if possible, bearing in mind that they can be recreated at boot time, i.e. they don't need to be persistent. ta, l. -- -- <a href="http://lkcl.net">http://lkcl.net</a> -- ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/xen-devel
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