Re: [PATCH v3] mm/page_alloc: detect allocation forbidden by cpuset and bail out early
From: Michal Hocko <mhocko@suse.com>
Date: 2021-09-15 11:30:36
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On Wed 15-09-21 13:32:47, Feng Tang wrote:
On Tue, Sep 14, 2021 at 05:30:03PM -0700, David Rientjes wrote:
[...]
quoted
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.
quoted hunk ↗ jump to hunk
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!
+ if (is_in_v2_mode()) hotplug_update_tasks(cs, &new_cpus, &new_mems, cpus_updated, mems_updated); Thanks, Feng
-- Michal Hocko SUSE Labs