Hi all, I have added the memory limit option in menu.lst of grub of Domain 0 like /boot/*xen*.gz dom0_max_vcpus=1 *dom0_mem*=1024M The domain 0 under xen can limit to 1024M. Now, I want to increase Domain 0 memory to 4GB and I have used xm mem-set command to increase Domain 0 memory. However, top of Domain0 still shows 1GB ram. Any help on it without rebooting server? Thanks! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi, The dom0_mem parameter locks the dom0 memory to the given amount (which is good for performance). You cannot balloon it at runtime. According to the documentation (and experiments) you should also pin dom0 to use specific cpus and keep domUs off those reserved cpus. HTH, Peter On 14.2.2012 4:44, KC LO wrote:> Hi all, > > I have added the memory limit option in menu.lst of grub of Domain 0 like > > /boot/*xen*.gz dom0_max_vcpus=1 *dom0_mem*=1024M > > The domain 0 under xen can limit to 1024M. Now, I want to increase Domain > 0 memory to 4GB and I have used xm mem-set command to increase Domain 0 > memory. However, top of Domain0 still shows 1GB ram. Any help on it > without rebooting server? > > Thanks! > > > This body part will be downloaded on demand._______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi,> The dom0_mem parameter locks the dom0 memory to the given amount > (which is good for performance). You cannot balloon it at runtime. > According to the documentation (and experiments) you should also pin > dom0 to use specific cpus and keep domUs off those reserved cpus.Yes, one can balloon dom0, see below. What made you think otherwise? Are you using a Xen version that has been built before 2006? There are enough misunderstandings already wrt Xen. So please just don''t answer unless you''re certain or else say "I THINK that ..." Also, you say locking dom0 memory is good for performance? Why? Do give us some reasoning to support this apparent "fact". Does it apply under all circumstances? Then dom0 CPU pinning. dom0_max_vcpus=1 is enough to have dom0 use one CPU. You don''t *have* to pin the CPU. Maybe you want to share one of your Quadcore CPU cores sometimes but not all the time. False info is so much more annoying than no info at all. Anyway. KC, the syntax for dom0_mem can be specified as follows: dom0_mem=[min:<min_amt>,][max:<max_amt>,][<amt>] example: dom0_mem=min:1G,max:4G,1G dom0_mem=min:1G,max:-1G,1G The second example explained: if your system has 16G RAM then you allow dom0 to use 15G at most. <min_amt>: The minimum amount of memory which should be allocated for dom0. <max_amt>: The maximum amount of memory which should be allocated for dom0. <amt>: The precise amount of memory to allocate for dom0. Notes: 1. <amt> is clamped from below by <min_amt> and from above by available memory and <max_amt> 2. <min_amt> is clamped from above by available memory and <max_amt> 3. <min_amt> is ignored if it is greater than <max_amt> 4. If <amt> is not specified, it is calculated as follows: "All of memory is allocated to domain 0, minus 1/16th which is reserved for uses such as DMA buffers (the reservation is clamped to 128MB)." Each value can be specified as positive or negative: If +ve: The specified amount is an absolute value. If -ve: The specified amount is subtracted from total available memory. This has been commited in 2006, see xen-unstable commit 2191:444496ecb14e.
Hi Mark, For example see this: http://fclose.com/b/linux/2258/managing-xen-dom0s-cpu-and-memory/ There''s lots of other information recommending to avoid ballooning of dom0 memory. That it is possible, doesn''t necessary imply that it''s a good thing. I notice performance improvements and "smoothness" in the Xen system, giving dom0 a fixed amount of memory and pinning a couple of cores for exclusive use by dom0. Peter On 14.2.2012 11:34, Mark van Dijk wrote:> Hi, > >> The dom0_mem parameter locks the dom0 memory to the given amount >> (which is good for performance). You cannot balloon it at runtime. >> According to the documentation (and experiments) you should also pin >> dom0 to use specific cpus and keep domUs off those reserved cpus. > Yes, one can balloon dom0, see below. What made you think otherwise? Are > you using a Xen version that has been built before 2006? > > There are enough misunderstandings already wrt Xen. So please just > don''t answer unless you''re certain or else say "I THINK that ..." > > Also, you say locking dom0 memory is good for performance? Why? Do give > us some reasoning to support this apparent "fact". Does it apply under > all circumstances? > > Then dom0 CPU pinning. dom0_max_vcpus=1 is enough to have dom0 use > one CPU. You don''t *have* to pin the CPU. Maybe you want to share one > of your Quadcore CPU cores sometimes but not all the time. > > False info is so much more annoying than no info at all. > > Anyway. > > KC, the syntax for dom0_mem can be specified as follows: > > dom0_mem=[min:<min_amt>,][max:<max_amt>,][<amt>] > > example: > dom0_mem=min:1G,max:4G,1G > dom0_mem=min:1G,max:-1G,1G > > The second example explained: if your system has 16G RAM then you allow > dom0 to use 15G at most. > > <min_amt>: The minimum amount of memory which should be allocated for dom0. > <max_amt>: The maximum amount of memory which should be allocated for dom0. > <amt>: The precise amount of memory to allocate for dom0. > > Notes: > 1.<amt> is clamped from below by<min_amt> and from above by available > memory and<max_amt> > 2.<min_amt> is clamped from above by available memory and<max_amt> > 3.<min_amt> is ignored if it is greater than<max_amt> > 4. If<amt> is not specified, it is calculated as follows: > "All of memory is allocated to domain 0, minus 1/16th which is reserved > for uses such as DMA buffers (the reservation is clamped to 128MB)." > > Each value can be specified as positive or negative: > If +ve: The specified amount is an absolute value. > If -ve: The specified amount is subtracted from total available memory. > > This has been commited in 2006, see xen-unstable commit > 2191:444496ecb14e. > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.1913 / Virus Database: 2112/4808 - Release Date: 02/13/12
Hi,> For example see this: > http://fclose.com/b/linux/2258/managing-xen-dom0s-cpu-and-memory/ > > There''s lots of other information recommending to avoid ballooning of > dom0 memory. That it is possible, doesn''t necessary imply that it''s a > good thing.In general, and applicable to the article above, it''s indeed wise to avoid ballooning *down* and/or *automatically*. It''s not about avoiding ballooning at all costs, although this does seem to be the common idea. I still consider it a wrongful interpretation as there''s no objection to manual ballooning, up or down, for as far as I know. In the article I also read: "Even after booting the system, the VCPU number can be configured by xm command. We can set Domain-0 have two VCPUs and processor 0 and 1 to be dedicated to Dom0 by these commands:" Have you ever tried to do this with dom0_vcpus_pin? Because if my systems boot with ''dom0_max_vcpus=1 dom0_vcpus_pin'' I can''t give them an extra core later on. So either the article is false or my system refuses things that his system allows.> I notice performance improvements and "smoothness" in the Xen system, > giving dom0 a fixed amount of memory and pinning a couple of cores > for exclusive use by dom0.That''s my point. Allocating a core for exclusive use by dom0 does not mean you need to pin them. If I pin the vcpus then I cannot raise/lower the amount of vcpus. So I am not disagreeing with you that you notice performance improvements. My whole point there was about (not) having to pin them.