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SubjectRe: [PATCH 4/5] cgroup: remove extra calls to find_existing_css_set
Tejun Heo (tj@kernel.org) wrote:
> Hello,
>
> On Tue, Dec 20, 2011 at 03:14:32PM -0800, Mandeep Singh Baines wrote:
> > @@ -1942,9 +1917,17 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> > }
> > }
> >
> > - retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
> > - if (retval)
> > + task_lock(tsk);
> > + oldcg = tsk->cgroups;
> > + task_unlock(tsk);
>
> Probably this is patch order issue w/ Frederic's patch but we don't
> need task_lock here, right?
>

Yeah, avoided removing the locks because Frederic's patch already did that.
Once his changes get in, I'll rebase and resend.

> > @@ -2171,17 +2088,18 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
> > * step 2: make sure css_sets exist for all threads to be migrated.
> > * we use find_css_set, which allocates a new one if necessary.
> > */
> > - INIT_LIST_HEAD(&newcg_list);
> > for (i = 0; i < group_size; i++) {
> > tc = flex_array_get(group, i);
> > /* get old css_set pointer */
> > task_lock(tc->task);
> > oldcg = tc->task->cgroups;
> > task_unlock(tc->task);
> > - /* if we don't already have it in the list get a new one */
> > - if (!css_set_fetched(cgrp, tc->task, oldcg, &newcg_list))
> > - if (retval = css_set_prefetch(cgrp, oldcg, &newcg_list))
> > - goto out_list_teardown;
> > + tc->cg = find_css_set(oldcg, cgrp);
> > + if (!tc->cg) {
> > + retval = -ENOMEM;
> > + css_set_refs = i + 1;
> > + goto out_list_teardown;
> > + }
>
> Nice cleanup, but can't the above be merged into the loop which builds
> the flex array?
>

Good idea. That would remove a for loop. Will fix in next version.

> Thanks.
>
> --
> tejun


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