| From foo@baz Mon Apr 9 17:09:24 CEST 2018 |
| From: Vlastimil Babka <vbabka@suse.cz> |
| Date: Mon, 15 May 2017 15:13:16 +0200 |
| Subject: sched/numa: Use down_read_trylock() for the mmap_sem |
| |
| From: Vlastimil Babka <vbabka@suse.cz> |
| |
| |
| [ Upstream commit 8655d5497735b288f8a9b458bd22e7d1bf95bb61 ] |
| |
| A customer has reported a soft-lockup when running an intensive |
| memory stress test, where the trace on multiple CPU's looks like this: |
| |
| RIP: 0010:[<ffffffff810c53fe>] |
| [<ffffffff810c53fe>] native_queued_spin_lock_slowpath+0x10e/0x190 |
| ... |
| Call Trace: |
| [<ffffffff81182d07>] queued_spin_lock_slowpath+0x7/0xa |
| [<ffffffff811bc331>] change_protection_range+0x3b1/0x930 |
| [<ffffffff811d4be8>] change_prot_numa+0x18/0x30 |
| [<ffffffff810adefe>] task_numa_work+0x1fe/0x310 |
| [<ffffffff81098322>] task_work_run+0x72/0x90 |
| |
| Further investigation showed that the lock contention here is pmd_lock(). |
| |
| The task_numa_work() function makes sure that only one thread is let to perform |
| the work in a single scan period (via cmpxchg), but if there's a thread with |
| mmap_sem locked for writing for several periods, multiple threads in |
| task_numa_work() can build up a convoy waiting for mmap_sem for read and then |
| all get unblocked at once. |
| |
| This patch changes the down_read() to the trylock version, which prevents the |
| build up. For a workload experiencing mmap_sem contention, it's probably better |
| to postpone the NUMA balancing work anyway. This seems to have fixed the soft |
| lockups involving pmd_lock(), which is in line with the convoy theory. |
| |
| Signed-off-by: Vlastimil Babka <vbabka@suse.cz> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Acked-by: Rik van Riel <riel@redhat.com> |
| Acked-by: Mel Gorman <mgorman@techsingularity.net> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Link: http://lkml.kernel.org/r/20170515131316.21909-1-vbabka@suse.cz |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/sched/fair.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/kernel/sched/fair.c |
| +++ b/kernel/sched/fair.c |
| @@ -2429,7 +2429,8 @@ void task_numa_work(struct callback_head |
| return; |
| |
| |
| - down_read(&mm->mmap_sem); |
| + if (!down_read_trylock(&mm->mmap_sem)) |
| + return; |
| vma = find_vma(mm, start); |
| if (!vma) { |
| reset_ptenuma_scan(p); |