Re: [libvirt] [PATCH] cgroup: Enable memory.use_hierarchy of cgroup for domain

On Thu, May 6, 2010 at 7:40 PM, Ryota Ozaki <ozaki.ryota(a)gmail.com&gt; wrote: > Through conversation with Kumar L Srikanth-B22348, I found > that the function of getting memory usage (e.g., virsh dominfo) > doesn't work for lxc with ns subsystem of cgroup enabled. > > This is because of features of ns and memory subsystems. > Ns creates child cgroup on every process fork and as a result > processes in a container are not assigned in a cgroup for > domain (e.g., libvirt/lxc/test1/). For example, libvirt_lxc > and init (or somewhat specified in XML) are assigned into > libvirt/lxc/test1/8839/ and libvirt/lxc/test1/8839/8849/, > respectively. On the other hand, memory subsystem accounts > memory usage within a group of processes by default, i.e., > it does not take any child (and descendent) groups into > account. With the two features, virsh dominfo which just > checks memory usage of a cgroup for domain always returns > zero because the cgroup has no process. > > Setting memory.use_hierarchy of a group allows to account > (and limit) memory usage of every descendent groups of the group. > By setting it of a cgroup for domain, we can get proper memory > usage of lxc with ns subsystem enabled. (To be exact, the > setting is required only when memory and ns subsystems are > enabled at the same time, e.g., mount -t cgroup none /cgroup.) > --- This does sound like a valid use case and the correct fix. >  src/util/cgroup.c |   49 +++++++++++++++++++++++++++++++++++++++++++++---- >  1 files changed, 45 insertions(+), 4 deletions(-) > > diff --git a/src/util/cgroup.c b/src/util/cgroup.c > index b8b2eb5..93cd6a9 100644 > --- a/src/util/cgroup.c > +++ b/src/util/cgroup.c > @@ -443,7 +443,38 @@ static int virCgroupCpuSetInherit(virCgroupPtr parent, virCgroupPtr group) >     return rc; >  } > > -static int virCgroupMakeGroup(virCgroupPtr parent, virCgroupPtr group, int create) > +static int virCgroupSetMemoryUseHierarchy(virCgroupPtr group) > +{ > +    int rc = 0; > +    unsigned long long value; > +    const char *filename = "memory.use_hierarchy"; > + > +    rc = virCgroupGetValueU64(group, > +                              VIR_CGROUP_CONTROLLER_MEMORY, > +                              filename, &value); > +    if (rc != 0) { > +        VIR_ERROR("Failed to read %s/%s (%d)", group->path, filename, rc); > +        return rc; > +    } > + > +    /* Setting twice causes error, so if already enabled, skip setting */ > +    if (value == 1) > +        return 0; > + > +    VIR_DEBUG("Setting up %s/%s", group->path, filename); > +    rc = virCgroupSetValueU64(group, > +                              VIR_CGROUP_CONTROLLER_MEMORY, > +                              filename, 1); > + > +    if (rc != 0) { > +        VIR_ERROR("Failed to set %s/%s (%d)", group->path, filename, rc); > +    } > + > +    return rc; > +} > + > +static int virCgroupMakeGroup(virCgroupPtr parent, virCgroupPtr group, > +                              int create, int memory_hierarchy) >  { >     int i; >     int rc = 0; > @@ -477,6 +508,16 @@ static int virCgroupMakeGroup(virCgroupPtr parent, virCgroupPtr group, int creat >                     break; >                 } >             } Can you please add a comment here stating that memory.use_hierarchy should always be called prior to creating subcgroups and attaching tasks

> +            if (memory_hierarchy && > +                group->controllers[VIR_CGROUP_CONTROLLER_MEMORY].mountPoint != NULL && > +                (i == VIR_CGROUP_CONTROLLER_MEMORY || > +                 STREQ(group->controllers[i].mountPoint, group->controllers[VIR_CGROUP_CONTROLLER_MEMORY].mountPoint))) { > +                rc = virCgroupSetMemoryUseHierarchy(group); > +                if (rc != 0) { > +                    VIR_FREE(path); > +                    break; > +                } > +            } >         } > >         VIR_FREE(path); > @@ -553,7 +594,7 @@ static int virCgroupAppRoot(int privileged, >     if (rc != 0) >         goto cleanup; > > -    rc = virCgroupMakeGroup(rootgrp, *group, create); > +    rc = virCgroupMakeGroup(rootgrp, *group, create, 0); > >  cleanup: >     virCgroupFree(&rootgrp); > @@ -653,7 +694,7 @@ int virCgroupForDriver(const char *name, >     VIR_FREE(path); > >     if (rc == 0) { > -        rc = virCgroupMakeGroup(rootgrp, *group, create); > +        rc = virCgroupMakeGroup(rootgrp, *group, create, 0); >         if (rc != 0) >             virCgroupFree(group); >     } > @@ -703,7 +744,7 @@ int virCgroupForDomain(virCgroupPtr driver, >     VIR_FREE(path); > >     if (rc == 0) { > -        rc = virCgroupMakeGroup(driver, *group, create); > +        rc = virCgroupMakeGroup(driver, *group, create, 1); >         if (rc != 0) >             virCgroupFree(group); >     } A comment on why Domains get hierarchy support and Drivers don't will help unless it is very obvious to developers.

Balbir