On Tue, Jan 08, 2013 at 04:42:00PM +0100, Michal Privoznik wrote: > On 08.01.2013 16:24, Daniel P. Berrange wrote: > > On Tue, Jan 08, 2013 at 10:37:19AM +0100, Michal Privoznik wrote: > >> Currently, if there's no hard memory limit defined for a domain, > >> libvirt tries to calculate one, based on domain definition and magic > >> equation and set it upon the domain startup. The rationale behind was, > >> if there's a memory leak or exploit in qemu, we should prevent the > >> host system trashing. However, the equation was too tightening, as it > >> didn't reflect what the kernel counts into the memory used by a > >> process. Since many hosts do have a swap, nobody hasn't noticed > >> anything, because if hard memory limit is reached, process can > >> continue allocating memory on a swap. However, if there is no swap on > >> the host, the process gets killed by OOM killer. In our case, the qemu > >> process it is. > >> > >> To prevent this, we need to relax the hard RSS limit. Moreover, we > >> should reflect more precisely the kernel way of accounting the memory > >> for process. That is, even the kernel caches are counted within the > >> memory used by a process (within cgroups at least). Hence the magic > >> equation has to be changed: > >> > >> limit = 1.5 * (domain memory + total video memory) + (32MB for cache > >> per each disk) + 200MB > >> --- > >> > >> There is a bit more that should be taken into account, e.g. shared > >> pages, where accounting is even more complicated: > >> > >> "Shared pages are accounted on the basis of the first touch approach. > >> The cgroup that first touches a page is accounted for the page." [1] > >> > >> I don't we even want to try to reflect this in our code. That's why > >> the coefficient of domain memory has been lifted from 1.02 to 1.5, in > >> hope it will just be enough. > >> > >> 1: http://www.kernel.org/doc/Documentation/cgroups/memory.txt > >> > >> src/qemu/qemu_cgroup.c | 15 +++++++++------ > >> 1 file changed, 9 insertions(+), 6 deletions(-) > >> > >> diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c > >> index 7faf025..16a9d7c 100644 > >> --- a/src/qemu/qemu_cgroup.c > >> +++ b/src/qemu/qemu_cgroup.c > >> @@ -343,15 +343,18 @@ int qemuSetupCgroup(virQEMUDriverPtr driver, > >> unsigned long long hard_limit = vm->def->mem.hard_limit; > >> > >> if (!hard_limit) { > >> - /* If there is no hard_limit set, set a reasonable > >> - * one to avoid system trashing caused by exploited qemu. > >> - * As 'reasonable limit' has been chosen: > >> - * (1 + k) * (domain memory + total video memory) + F > >> - * where k = 0.02 and F = 200MB. */ > >> + /* If there is no hard_limit set, set a reasonable one to avoid > >> + * system trashing caused by exploited qemu. As 'reasonable limit' > >> + * has been chosen: > >> + * (1 + k) * (domain memory + total video memory) + (32MB for > >> + * cache per each disk) + F > >> + * where k = 0.5 and F = 200MB. The cache for disks is important as > >> + * kernel cache on the host side counts into the RSS limit. */ > >> hard_limit = vm->def->mem.max_balloon; > >> for (i = 0; i < vm->def->nvideos; i++) > >> hard_limit += vm->def->videos[i]->vram; > >> - hard_limit = hard_limit * 1.02 + 204800; > >> + hard_limit = hard_limit * 1.5 + 204800; > >> + hard_limit += vm->def->ndisks * 32768; > >> } > >> > >> rc = virCgroupSetMemoryHardLimit(cgroup, hard_limit); > > > > ACK, > > > > can't say I'm a fan of our heuristics but I don't see a better way > > yet. Lets see how this new limit copes. > > > > Daniel > > > > Yeah, it's sort of magic. Pushed now. Thanks. How does one turn off the limits? Dave > Michal > > -- > libvir-list mailing list > libvir-list@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/libvir-list -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list