[PATCH] Fix KMALLOC_MAX_SIZE overflow during cpumask allocation

From: Alex Thorlton
Date: Tue Dec 02 2014 - 12:18:12 EST


When allocating space for load_balance_mask, in sched_init, when
CPUMASK_OFFSTACK is set, we've managed to spill over KMALLOC_MAX_SIZE on our
6144 core machine. The patch below breaks up the allocations so that they don't
overflow the max alloc size. It also allocates the masks on the the node from
which they'll most commonly be accessed, to minimize remote accesses on NUMA
machines.

Any input is appreciated!

- Alex

Signed-off-by: Alex Thorlton <athorlton@xxxxxxx>
Suggested-by: George Beshers <gbeshers@xxxxxxx>
Cc: George Beshers <gbeshers@xxxxxxx>
Cc: Russ Anderson <rja@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx

---
kernel/sched/core.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4499950..8f06655 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6981,9 +6981,6 @@ void __init sched_init(void)
#ifdef CONFIG_RT_GROUP_SCHED
alloc_size += 2 * nr_cpu_ids * sizeof(void **);
#endif
-#ifdef CONFIG_CPUMASK_OFFSTACK
- alloc_size += num_possible_cpus() * cpumask_size();
-#endif
if (alloc_size) {
ptr = (unsigned long)kzalloc(alloc_size, GFP_NOWAIT);

@@ -7003,12 +7000,10 @@ void __init sched_init(void)
ptr += nr_cpu_ids * sizeof(void **);

#endif /* CONFIG_RT_GROUP_SCHED */
-#ifdef CONFIG_CPUMASK_OFFSTACK
- for_each_possible_cpu(i) {
- per_cpu(load_balance_mask, i) = (void *)ptr;
- ptr += cpumask_size();
- }
-#endif /* CONFIG_CPUMASK_OFFSTACK */
+ }
+ for_each_possible_cpu(i) {
+ per_cpu(load_balance_mask, i) = kzalloc_node(
+ cpumask_size(), GFP_KERNEL, cpu_to_node(i));
}

init_rt_bandwidth(&def_rt_bandwidth,
--
1.7.12.4

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