From: "Mizuma, Masayoshi" <m.mizuma@xxxxxxxxxxxxxx>
Subject: mm: hugetlb: fix softlockup when a large number of hugepages are freed.
When I decrease the value of nr_hugepage in procfs a lot, softlockup
happens. It is because there is no chance of context switch during this
process.
On the other hand, when I allocate a large number of hugepages, there is
some chance of context switch. Hence softlockup doesn't happen during
this process. So it's necessary to add the context switch in the freeing
process as same as allocating process to avoid softlockup.
When I freed 12 TB hugapages with kernel-2.6.32-358.el6, the freeing
process occupied a CPU over 150 seconds and following softlockup message
appeared twice or more.
$ echo 6000000 > /proc/sys/vm/nr_hugepages
$ cat /proc/sys/vm/nr_hugepages
6000000
$ grep ^Huge /proc/meminfo
HugePages_Total: 6000000
HugePages_Free: 6000000
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
$ echo 0 > /proc/sys/vm/nr_hugepages
BUG: soft lockup - CPU#16 stuck for 67s! [sh:12883] ...
Pid: 12883, comm: sh Not tainted 2.6.32-358.el6.x86_64 #1
Call Trace:
[<ffffffff8115a438>] ? free_pool_huge_page+0xb8/0xd0
[<ffffffff8115a578>] ? set_max_huge_pages+0x128/0x190
[<ffffffff8115c663>] ? hugetlb_sysctl_handler_common+0x113/0x140
[<ffffffff8115c6de>] ? hugetlb_sysctl_handler+0x1e/0x20
[<ffffffff811f3097>] ? proc_sys_call_handler+0x97/0xd0
[<ffffffff811f30e4>] ? proc_sys_write+0x14/0x20
[<ffffffff81180f98>] ? vfs_write+0xb8/0x1a0
[<ffffffff81181891>] ? sys_write+0x51/0x90
[<ffffffff810dc565>] ? __audit_syscall_exit+0x265/0x290
[<ffffffff8100b072>] ? system_call_fastpath+0x16/0x1b
I have not confirmed this problem with upstream kernels because I am not
able to prepare the machine equipped with 12TB memory now. However I
confirmed that the amount of decreasing hugepages was directly
proportional to the amount of required time.
I measured required times on a smaller machine. It showed 130-145
hugepages decreased in a millisecond.
Amount of decreasing Required time Decreasing rate
hugepages (msec) (pages/msec)
------------------------------------------------------------
10,000 pages == 20GB 70 - 74 135-142
30,000 pages == 60GB 208 - 229 131-144
It means decrement of 6TB hugepages will trigger softlockup with the
default threshold 20sec, in this decreasing rate.
Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Cc: Aneesh Kumar <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 1 +
1 file changed, 1 insertion(+)
diff -puN mm/hugetlb.c~mm-hugetlb-fix-softlockup-when-a-large-number-of-hugepages-are-freed mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-fix-softlockup-when-a-large-number-of-hugepages-are-freed
+++ a/mm/hugetlb.c
@@ -1536,6 +1536,7 @@ static unsigned long set_max_huge_pages(
while (min_count < persistent_huge_pages(h)) {
if (!free_pool_huge_page(h, nodes_allowed, 0))
break;
+ cond_resched_lock(&hugetlb_lock);
}
while (count < persistent_huge_pages(h)) {
if (!adjust_pool_surplus(h, nodes_allowed, 1))
_
--
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