Hi, The 4Gb memory limit with Xen on x86 may prove to be a real issue to us. So I was wondering, are there any approaches that might not require too much work to support more than 4Gb of physical memory on a machine? For example, could all machines run in more or less HIGHMEM style mode (perhaps using PSE36 or PAE), and still share the paging tables as normally happens in Xen? In short - what would be the easiest approach to supporting more than 4Gb of physical memory in Xen and how much work would you estimate it to be? -- Naked ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
> The 4Gb memory limit with Xen on x86 may prove to be a real issue to > us. So I was wondering, are there any approaches that might not > require too much work to support more than 4Gb of physical memory on a > machine? > > For example, could all machines run in more or less HIGHMEM style mode > (perhaps using PSE36 or PAE), and still share the paging tables as > normally happens in Xen? > > In short - what would be the easiest approach to supporting more than > 4Gb of physical memory in Xen and how much work would you estimate it > to be?You''d need to modify both Xen and the guest to understand PAE36 mode. Not rocket science, but a fair sized chunk of work. BTW: x86''s loose about 5% of performance operating in PAE36 mode. In short, we don''t think it''s worth the effort: it''s much better to switch to x86_64. I doubt there are that many x86 boxes out there with more than 4GB of memory that this decision is going to effect. It''s certainly not possible to buy a new server that isn''t x86_64 these days... Ian ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
On Mon, 29 Nov 2004, Nuutti Kotivuori wrote:> In short - what would be the easiest approach to supporting more than > 4Gb of physical memory in Xen and how much work would you estimate it to > be?Xen and the OSes you run as guests both need to have the architecture support for PAE mode. A lot of the needed code can be cut''n''pasted from linux/include/asm-i386 and linux/arch/i386 so it should probably be about a month of work. Maybe less for somebody familiar with the internals of both Xen and the architecture dependant code in Linux. -- "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." - Brian W. Kernighan ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
Ian Pratt wrote:> You''d need to modify both Xen and the guest to understand PAE36 > mode. Not rocket science, but a fair sized chunk of work. BTW: > x86''s loose about 5% of performance operating in PAE36 mode.Right.> In short, we don''t think it''s worth the effort: it''s much better > to switch to x86_64. I doubt there are that many x86 boxes out > there with more than 4GB of memory that this decision is going to > effect. It''s certainly not possible to buy a new server that > isn''t x86_64 these days...Well, the hardware in question would be IBM server hardware with 16 gigabytes of memory. x86_64 is still a new technology and EM64T processors are not readily available. And your x86_64 support is scheduled for April in any case. These are hardly things one can depend on. But yeah, I understand that it might not be worth the effort if it is no small tweak. Just exploring all the options here. -- Naked ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
On Mon, 29 Nov 2004, Nuutti Kotivuori wrote:> The 4Gb memory limit with Xen on x86 may prove to be a real issue to > us. So I was wondering, are there any approaches that might not > require too much work to support more than 4Gb of physical memory on a > machine?wouldn''t getting x86-64 be the best route long term? ron ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
Ronald G. Minnich wrote:> On Mon, 29 Nov 2004, Nuutti Kotivuori wrote: >> The 4Gb memory limit with Xen on x86 may prove to be a real issue >> to us. So I was wondering, are there any approaches that might not >> require too much work to support more than 4Gb of physical memory >> on a machine? > > wouldn''t getting x86-64 be the best route long term?When dealing with customers, picking hardware is not always possible. Also, long term still leaves atleast 6 months where an alternate selection would be needed. So, yes, you are right, x86_64 will be the best solution in the long term. Regular x86 with more than 4Gb memory will most likely fade into obscurity. -- Naked ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel