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    SubjectRe: [PATCH v2 26/33] Task fork and exit for rdtgroup
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    On 09/08/2016 02:57 AM, Fenghua Yu wrote:
    > +void rdtgroup_fork(struct task_struct *child)
    > +{
    > + struct rdtgroup *rdtgrp;
    > +
    > + INIT_LIST_HEAD(&child->rg_list);
    > + if (!rdtgroup_mounted)
    > + return;
    > +
    > + mutex_lock(&rdtgroup_mutex);
    > +
    > + rdtgrp = current->rdtgroup;
    > + if (!rdtgrp)
    > + goto out;
    > +
    > + list_add_tail(&child->rg_list, &rdtgrp->pset.tasks);
    > + child->rdtgroup = rdtgrp;
    > + atomic_inc(&rdtgrp->refcount);
    > +
    > +out:
    > + mutex_unlock(&rdtgroup_mutex);
    > +}
    ...
    > diff --git a/kernel/fork.c b/kernel/fork.c
    > index beb3172..79bfc99 100644
    > --- a/kernel/fork.c
    > +++ b/kernel/fork.c
    > @@ -76,6 +76,7 @@
    > #include <linux/compiler.h>
    > #include <linux/sysctl.h>
    > #include <linux/kcov.h>
    > +#include <linux/resctrl.h>
    >
    > #include <asm/pgtable.h>
    > #include <asm/pgalloc.h>
    > @@ -1426,6 +1427,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
    > p->io_context = NULL;
    > p->audit_context = NULL;
    > cgroup_fork(p);
    > + rdtgroup_fork(p);
    > #ifdef CONFIG_NUMA
    > p->mempolicy = mpol_dup(p->mempolicy);
    > if (IS_ERR(p->mempolicy)) {

    Yikes, is this a new global lock and possible atomic_inc() on a shared
    variable in the fork() path? Has there been any performance or
    scalability testing done on this code?

    That mutex could be a disaster for fork() once the filesystem is
    mounted. Even if it goes away, if you have a large number of processes
    in an rdtgroup and they are forking a lot, you're bound to see the
    rdtgrp->refcount get bounced around a lot.

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