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Re: [libvirt] [PATCH] qemu: Set reasonable RSS limit on domain startup



On Tue, Jul 17, 2012 at 11:14:43PM -0500, Doug Goldstein wrote:
> On Tue, Jul 17, 2012 at 11:45 AM, Michal Privoznik <mprivozn redhat com> wrote:
> > If there's a memory leak in qemu or qemu is exploited the host's
> > system will sooner or later start trashing instead of killing
> > the bad process. This however has impact on performance and other
> > guests as well. Therefore we should set a reasonable RSS limit
> > even when user hasn't set any. It's better to be secure by default.
> > ---
> >  src/qemu/qemu_cgroup.c |   73 +++++++++++++++++++++++++++---------------------
> >  1 files changed, 41 insertions(+), 32 deletions(-)
> >
> > diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
> > index e39f5e1..2c158c1 100644
> > --- a/src/qemu/qemu_cgroup.c
> > +++ b/src/qemu/qemu_cgroup.c
> > @@ -339,42 +339,51 @@ int qemuSetupCgroup(struct qemud_driver *driver,
> >          }
> >      }
> >
> > -    if (vm->def->mem.hard_limit != 0 ||
> > -        vm->def->mem.soft_limit != 0 ||
> > -        vm->def->mem.swap_hard_limit != 0) {
> > -        if (qemuCgroupControllerActive(driver, VIR_CGROUP_CONTROLLER_MEMORY)) {
> > -            if (vm->def->mem.hard_limit != 0) {
> > -                rc = virCgroupSetMemoryHardLimit(cgroup, vm->def->mem.hard_limit);
> > -                if (rc != 0) {
> > -                    virReportSystemError(-rc,
> > -                                         _("Unable to set memory hard limit for domain %s"),
> > -                                         vm->def->name);
> > -                    goto cleanup;
> > -                }
> > -            }
> > -            if (vm->def->mem.soft_limit != 0) {
> > -                rc = virCgroupSetMemorySoftLimit(cgroup, vm->def->mem.soft_limit);
> > -                if (rc != 0) {
> > -                    virReportSystemError(-rc,
> > -                                         _("Unable to set memory soft limit for domain %s"),
> > -                                         vm->def->name);
> > -                    goto cleanup;
> > -                }
> > +    if (qemuCgroupControllerActive(driver, VIR_CGROUP_CONTROLLER_MEMORY)) {
> > +        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) + F
> > +             * where k = 0.02 and F = 200MB. */
> > +            hard_limit = vm->def->mem.max_balloon * 1.02 + 204800;
> > +        }
> > +
> > +        rc = virCgroupSetMemoryHardLimit(cgroup, hard_limit);
> > +        if (rc != 0) {
> > +            virReportSystemError(-rc,
> > +                                 _("Unable to set memory hard limit for domain %s"),
> > +                                 vm->def->name);
> > +            goto cleanup;
> > +        }
> > +        if (vm->def->mem.soft_limit != 0) {
> > +            rc = virCgroupSetMemorySoftLimit(cgroup, vm->def->mem.soft_limit);
> > +            if (rc != 0) {
> > +                virReportSystemError(-rc,
> > +                                     _("Unable to set memory soft limit for domain %s"),
> > +                                     vm->def->name);
> > +                goto cleanup;
> >              }
> > +        }
> >
> > -            if (vm->def->mem.swap_hard_limit != 0) {
> > -                rc = virCgroupSetMemSwapHardLimit(cgroup, vm->def->mem.swap_hard_limit);
> > -                if (rc != 0) {
> > -                    virReportSystemError(-rc,
> > -                                         _("Unable to set swap hard limit for domain %s"),
> > -                                         vm->def->name);
> > -                    goto cleanup;
> > -                }
> > +        if (vm->def->mem.swap_hard_limit != 0) {
> > +            rc = virCgroupSetMemSwapHardLimit(cgroup, vm->def->mem.swap_hard_limit);
> > +            if (rc != 0) {
> > +                virReportSystemError(-rc,
> > +                                     _("Unable to set swap hard limit for domain %s"),
> > +                                     vm->def->name);
> > +                goto cleanup;
> >              }
> > -        } else {
> > -            qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> > -                            _("Memory cgroup is not available on this host"));
> >          }
> > +    } else if (vm->def->mem.hard_limit != 0 ||
> > +               vm->def->mem.soft_limit != 0 ||
> > +               vm->def->mem.swap_hard_limit != 0) {
> > +        qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> > +                        _("Memory cgroup is not available on this host"));
> > +    } else {
> > +        VIR_WARN("Could not autoset a RSS limit for domain %s", vm->def->name);
> >      }
> >
> >      if (vm->def->cputune.shares != 0) {
> > --
> > 1.7.8.6
> >
> 
> Looks like a good change. My only question would be if its better to
> look up the guest video RAM instead of assuming that QEMU overhead +
> guest video RAM will amount to no more than about 200MB (I say about
> because of the 1.02 fudge factor). If its not really possible to grab
> that or it just makes sense to go with a set value like this then ACK
> from me.

Yeah, since we go to the trouble of keeping video RAM in the XML, I
say we ought to use it, instead of the 200MB fudge factor.


Daniel
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