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SubjectRe: [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy
Hi Qian,

On Tue, May 26, 2020 at 10:25:39PM -0400, Qian Cai wrote:
> > > > > [1] https://lkml.org/lkml/2020/3/5/57
> > > >
> > > > Reverted this series fixed a warning under memory pressue.
> > >
> > > Andrew, Stephen, can you drop this series?
> > >
> > > >
> > > > [ 3319.257898] LTP: starting oom01
> > > > [ 3319.284417] ------------[ cut here ]------------
> > > > [ 3319.284439] memory commitment underflow
> >
> > Thanks for the catch!
> >
> > Could you share the info about the platform, like the CPU numbers
> > and RAM size, and what's the mmap test size of your test program.
> > It would be great if you can point me the link to the test program.
>
> I have been reproduced this on both AMD and Intel. The test just
> allocating memory and swapping.
>
> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/oom/oom01.c
> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/tunable/overcommit_memory.c
>
> It might be better to run the whole LTP mm tests if none of the above
> triggers it for you which has quite a few memory pressurers.
>
> /opt/ltp/runltp -f mm

Thanks for sharing. I tried to reproduce this on 2 server plaforms,
but can't reproduce it, and they are still under testing.

Meanwhile, could you help to try the below patch, which is based on
Andi's suggestion and have some debug info. The warning is a little
strange, as the condition is

(percpu_counter_read(&vm_committed_as) <
-(s64)vm_committed_as_batch * num_online_cpus())

while for your platform (48 CPU + 128 GB RAM), the
'-(s64)vm_committed_as_batch * num_online_cpus()'
is a s64 value: '-32G', which makes the condition hard to be true,
and when it is, it could be triggered by some magic for s32/s64
operations around the percpu-counter.

Thanks,
Feng

---
mm/util.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 988d11e6c17c..2f3a2e0f12ae 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -797,10 +797,15 @@ EXPORT_SYMBOL_GPL(vm_memory_committed);
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
long allowed;
-
- VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
+ if (percpu_counter_read(&vm_committed_as) <
+ -(s64)vm_committed_as_batch * num_online_cpus()) {
+ printk("as:%lld as_sum:%lld check:%lld batch:%d\n",
+ percpu_counter_read(&vm_committed_as),
+ percpu_counter_sum(&vm_committed_as),
-(s64)vm_committed_as_batch * num_online_cpus(),
- "memory commitment underflow");
+ vm_committed_as_batch);
+
+ }

vm_acct_memory(pages);

@@ -816,6 +821,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
return 0;
}

+ VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
+ -(s64)vm_committed_as_batch * num_online_cpus(),
+ "memory commitment underflow");
+
allowed = vm_commit_limit();
/*
* Reserve some for root
--
2.14.1
>
> # lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Byte Order: Little Endian
> CPU(s): 48
> On-line CPU(s) list: 0-47
> Thread(s) per core: 1
> Core(s) per socket: 12
> Socket(s): 4
> NUMA node(s): 4
> Vendor ID: GenuineIntel
> CPU family: 6
> Model: 63
> Model name: Intel(R) Xeon(R) CPU E5-4650 v3 @ 2.10GHz
> Stepping: 2
> CPU MHz: 1198.498
> BogoMIPS: 4195.14
> Virtualization: VT-x
> L1d cache: 32K
> L1i cache: 32K
> L2 cache: 256K
> L3 cache: 30720K
> NUMA node0 CPU(s): 0-5,24-29
> NUMA node1 CPU(s): 6-11,30-35
> NUMA node2 CPU(s): 12-17,36-41
> NUMA node3 CPU(s): 18-23,42-47
>
> # numactl -H
> available: 4 nodes (0-3)
> node 0 cpus: 0 1 2 3 4 5 24 25 26 27 28 29
> node 0 size: 27768 MB
> node 0 free: 27539 MB
> node 1 cpus: 6 7 8 9 10 11 30 31 32 33 34 35
> node 1 size: 32225 MB
> node 1 free: 32009 MB
> node 2 cpus: 12 13 14 15 16 17 36 37 38 39 40 41
> node 2 size: 32253 MB
> node 2 free: 32174 MB
> node 3 cpus: 18 19 20 21 22 23 42 43 44 45 46 47
> node 3 size: 32252 MB
> node 3 free: 31330 MB
> node distances:
> node 0 1 2 3
> 0: 10 21 21 21
> 1: 21 10 21 21
> 2: 21 21 10 21
> 3: 21 21 21 10
>
> >
> > Thanks,
> > Feng
> >
> > > > [ 3319.284456] WARNING: CPU: 13 PID: 130949 at mm/util.c:835 __vm_enough_memory+0x1dc/0x1f0
> > > > [ 3319.284485] Modules linked in: brd ext4 crc16 mbcache jbd2 loop kvm_hv kvm ip_tables x_tables xfs sd_mod ahci libahci bnx2x libata mdio tg3 libphy firmware_class dm_mirror dm_region_hash dm_log dm_mod
> > > > [ 3319.284538] CPU: 13 PID: 130949 Comm: oom01 Not tainted 5.7.0-rc6-next-20200521+ #115
> > > > [ 3319.284551] NIP: c00000000043027c LR: c000000000430278 CTR: c0000000007bd120
> > > > [ 3319.284572] REGS: c00000064a42f710 TRAP: 0700 Not tainted (5.7.0-rc6-next-20200521+)
> > > > [ 3319.284602] MSR: 900000000282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28222422 XER: 20040000
> > > > [ 3319.284638] CFAR: c000000000119098 IRQMASK: 0
> > > > GPR00: c000000000430278 c00000064a42f9a0 c000000001765500 000000000000001b
> > > > GPR04: c00000000179c3b0 000000000000000b 0000000066726564 c00000000429ac28
> > > > GPR08: 0000000000000001 0000000000000000 0000000000000000 c000001301facc80
> > > > GPR12: 0000000000002000 c000001fffff3d80 0000000000000000 0000000000000000
> > > > GPR16: 0000000000000000 0000000000000000 c0000014f358dd60 fffffffffff7dfff
> > > > GPR20: c0000003725a9128 c0000003725a3928 c000000b0a0c0670 c000000b0a0c0678
> > > > GPR24: c000000b0a0c0660 c00000064a42fa58 c000000b0a0c0650 c0000003725a9080
> > > > GPR28: 0000000000000001 0000000000000000 c000000001620178 0000000000000001
> > > > [ 3319.284825] NIP [c00000000043027c] __vm_enough_memory+0x1dc/0x1f0
> > > > [ 3319.284853] LR [c000000000430278] __vm_enough_memory+0x1d8/0x1f0
> > > > [ 3319.284872] Call Trace:
> > > > [ 3319.284889] [c00000064a42f9a0] [c000000000430278] __vm_enough_memory+0x1d8/0x1f0 (unreliable)
> > > > [ 3319.284930] [c00000064a42fa30] [c000000000114258] dup_mm+0x2a8/0x700
> > > > [ 3319.284960] [c00000064a42fae0] [c000000000115c7c] copy_process+0xeac/0x1a00
> > > > [ 3319.284981] [c00000064a42fbf0] [c000000000116b3c] _do_fork+0xac/0xce0
> > > > [ 3319.285002] [c00000064a42fd00] [c000000000117928] __do_sys_clone+0x98/0xe0
> > > > [ 3319.285032] [c00000064a42fdc0] [c000000000039e78] system_call_exception+0x108/0x1d0
> > > > [ 3319.285064] [c00000064a42fe20] [c00000000000c9f0] system_call_common+0xf0/0x278
> > > > [ 3319.285093] Instruction dump:
> > > > [ 3319.285109] 60000000 73a90001 4182000c e8be0002 4bfffeb8 3c62ff51 39200001 3d42fff9
> > > > [ 3319.285142] 38636690 992a6ad6 4bce8dbd 60000000 <0fe00000> e8be0002 4bfffe90 60000000

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