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SubjectRe: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset and bail out early
On Wed, Sep 15, 2021 at 01:30:27PM +0200, Michal Hocko wrote:
> On Wed 15-09-21 13:32:47, Feng Tang wrote:
> > On Tue, Sep 14, 2021 at 05:30:03PM -0700, David Rientjes wrote:
> [...]
> > > I'm wondering about a single node nodemask, for example, where all
> > > ZONE_NORMAL memory is hot-removed.
>
> While this is theoretically possible it is highly unlikely to happen.
> Non movable memory just takes one kernel allocation to prevent any
> hotremove operation to finish. I have to say I was not aware of the
> hotplug callback. It all seems rather suspicious. I will have a look.
>
> Anyway something worth having covered "just in case". Thanks for
> pointing it out.
>
> > Thanks for the reminding! Yes, memory hot remove can change the
> > cpuset's effective nodemask, we may need to add similar check inside
> > cpuset_hotplug_update_tasks() which is called by cpuset_hotplug_workfn(),
> > something like below?
> >
> > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> > index 7fa633e..d5f6776 100644
> > --- a/kernel/cgroup/cpuset.c
> > +++ b/kernel/cgroup/cpuset.c
> > @@ -3186,6 +3186,14 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
> > cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
> > mems_updated = !nodes_equal(new_mems, cs->effective_mems);
> >
> > + if (mems_updated && !cpusets_insane_config() &&
> > + movable_only_nodes(new_mems)) {
> > + static_branch_enable(&cpusets_insane_config_key);
> > + pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl) after memory hotplug."
> > + "Cpuset allocations might fail even with a lot of memory available.\n",
> > + nodemask_pr_args(new_mems);
> > + }
>
> Please create a helper rather than two copies of the same. Thanks!

Sure. Some draft add-on patch below.

Thanks,
Feng

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7fa633e..3bb9f4ea 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -391,6 +391,18 @@ static inline bool is_in_v2_mode(void)
(cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
}

+static inline void check_insane_mems_config(nodemask_t *nodes)
+{
+ if (!cpusets_insane_config() &&
+ movable_only_nodes(nodes)) {
+ static_branch_enable(&cpusets_insane_config_key);
+ pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)! "
+ "Cpuset allocations might fail even with a lot of memory available.\n",
+ nodemask_pr_args(nodes));
+ }
+}
+
/*
* Return in pmask the portion of a task's cpusets's cpus_allowed that
* are online and are capable of running the task. If none are found,
@@ -1875,13 +1887,7 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
if (retval < 0)
goto done;

- if (!cpusets_insane_config() &&
- movable_only_nodes(&trialcs->mems_allowed)) {
- static_branch_enable(&cpusets_insane_config_key);
- pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)! "
- "Cpuset allocations might fail even with a lot of memory available.\n",
- nodemask_pr_args(&trialcs->mems_allowed));
- }
+ check_insane_mems_config(&trialcs->mems_allowed);

spin_lock_irq(&callback_lock);
cs->mems_allowed = trialcs->mems_allowed;
@@ -3186,6 +3192,9 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
mems_updated = !nodes_equal(new_mems, cs->effective_mems);

+ if (mems_updated)
+ check_insane_mems_config(&new_mems);
+
if (is_in_v2_mode())
hotplug_update_tasks(cs, &new_cpus, &new_mems,
cpus_updated, mems_updated);
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