Hi Daniel I understood your suggestion. Therefore, I decline applying this patch. Thanks, Masayuki Sunou. In message <20070322101643.GA21706@xxxxxxxxxx> "Re: [PATCH] Add the message when a little memory is set with setmaxmem." "Daniel Veillard <veillard@xxxxxxxxxx>" wrote: > On Thu, Mar 22, 2007 at 01:56:25PM +0900, Masayuki Sunou wrote: > > Hi > > > > The message which a cause of an error is hard to detect is displayed when > > "virsh setmaxmem" sets the maximum memory of an active domain less than > > Used Memory. > > > > -------------------------------------------------------------------------------- > > # virsh setmaxmem 0 4096 > > libvir: Xen error : failed Xen syscall ioctl 8518692 > > libvir: Xen Daemon error : POST operation failed: (xend.err "(22, 'Invalid argument')") > > libvir: error : library call virDomainSetMaxMemory failed, possibly not supported > > -------------------------------------------------------------------------------- > > > > This patch displays the message which is easier to detect the cause of > > an error to a user. > > > > -------------------------------------------------------------------------------- > > # virsh setmaxmem 0 4096 > > error: 4096 is less than current used memory. > > -------------------------------------------------------------------------------- > > Hum, this sounds useful from a user interraction perspective, but I > have a doubt about it, first it's a bit racy, i.e. the memory usage could > change between the GetInfo call and the SetMaxMem one, but my main problem > is that I'm afraid this would prevent the possibility of automatic memory > resize in some case. Assume a paravirtual guest kernel, supporting memory > resizing, then it could in theory shrink its memory footprint if asked for > (migrating dirty pages to swap dynamically for example). Such a mechanism > sounds important to load balance usage between multiple guests sharing a > host, and I'm afraid your patch would block that capacity just because > Xen does not accept that operation in that version. > I'm afraid that patch - even if limited to virsh - is unfortunately not > a good idea, as usual the preferred way would be to get xend fixed to > return a better error message, so I prefer to decline applying that patch > as is. I'm also wondering if virDomainSetMemory() should not be called first > to try to shrink and then only make the check of the current memory usage, > the problem is that memory shrinking is likely to be a long operation in > that case since it certainly gonna involve moving blocks to disk. > I Cc'ed Rik who may have a more complete opinion on guest memory shrinking. > > Daniel > > -- > Red Hat Virtualization group http://redhat.com/virtualization/ > Daniel Veillard | virtualization library http://libvirt.org/ > veillard@xxxxxxxxxx | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ > http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/