> On Jan 28, 2021, at 10:56 PM, George Dunlap <george.dun...@citrix.com> wrote: > > > >> On Jan 28, 2021, at 10:42 PM, George Dunlap <george.dun...@citrix.com> wrote: >> >> >> >>> On Jan 28, 2021, at 6:26 PM, Elliott Mitchell <ehem+...@m5p.com> wrote: >>> >>> On Thu, Jan 28, 2021 at 11:19:41AM +0100, Jan Beulich wrote: >>>> On 27.01.2021 23:28, Elliott Mitchell wrote: >>>>> On Wed, Jan 27, 2021 at 09:03:32PM +0000, Andrew Cooper wrote: >>>>>> So.?? What *should* happen is that if QEMU/OVMF dirties more memory than >>>>>> exists in the PoD cache, the domain gets terminated. >>>>>> >>>>>> Irrespective, Xen/dom0 dying isn't an expected consequence of any normal >>>>>> action like this. >>>>>> >>>>>> Do you have a serial log of the crash??? If not, can you set up a crash >>>>>> kernel environment to capture the logs, or alternatively reproduce the >>>>>> issue on a different box which does have serial? >>>>> >>>>> No, I don't. I'm setup to debug ARM failures, not x86 ones. >>>> >>>> Then alternatively can you at least give conditions that need to >>>> be met to observe the problem, for someone to repro and then >>>> debug? (The less complex the better, of course.) >>> >>> Multiple prior messages have included statements of what I believed to be >>> the minimal case to reproduce. Presently I believe the minimal >>> constraints are, maxmem >= host memory, memory < free Xen memory, type >>> HVM. A minimal kr45hme.cfg file: >>> >>> type = "hvm" >>> memory = 1024 >>> maxmem = 1073741824 >>> >>> I suspect maxmem > free Xen memory may be sufficient. The instances I >>> can be certain of have been maxmem = total host memory *7. >> >> Can you include your Xen version and dom0 command-line? >> >> For me, domain creation fails with an error like this: >> >> root@immortal:/images# xl create c6-01.cfg maxmem=1073741824 >> Parsing config from c6-01.cfg >> xc: error: panic: xc_dom_boot.c:120: xc_dom_boot_mem_init: can't allocate >> low memory for domain: Out of memory >> libxl: error: libxl_dom.c:593:libxl__build_dom: xc_dom_boot_mem_init failed: >> Cannot allocate memory >> libxl: error: libxl_create.c:1576:domcreate_rebuild_done: Domain 9:cannot >> (re-)build domain: -3 >> libxl: error: libxl_domain.c:1182:libxl__destroy_domid: Domain >> 9:Non-existant domain >> libxl: error: libxl_domain.c:1136:domain_destroy_callback: Domain 9:Unable >> to destroy guest >> libxl: error: libxl_domain.c:1063:domain_destroy_cb: Domain 9:Destruction of >> domain failed >> >> This is on staging-4.14 from a month or two ago (i.e., what I happened to >> have on a random test box), and `dom0_mem=1024M,max:1024M` in my >> command-line. That rune will give dom0 only 1GiB of RAM, but also prevent >> it from auto-ballooning down to free up memory for the guest. > > Hmm, but with that line removed, I get this: > > root@immortal:/images# xl create c6-01.cfg maxmem=1073741824 > Parsing config from c6-01.cfg > libxl: error: libxl_mem.c:279:libxl_set_memory_target: New target 0 for dom0 > is below the minimum threshold > failed to free memory for the domain > > Maybe the issue you’re probably facing is that “minimum threshold” safety > catch either isn’t triggering, or is set low enough that your dom0 is OOMing > trying to make enough memory for your VM?
Looks like LIBXL_MIN_DOM0_MEM is hard-coded to 128MiB, which is not going to be enough on a lot of systems. At very least that should be something that can be set in a global config somewhere. Ideally we’d have a more sophisticated way of calculating the minimum value that wouldn’t trip so easily. Elliot, as a short-term fix, I suggest considering setting aside a fixed amount of memory for dom0, as recommended in https://wiki.xenproject.org/wiki/Xen_Project_Best_Practices. -George
