Re: [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy

From: Qian Cai
Date: Tue May 26 2020 - 22:25:47 EST

On Wed, May 27, 2020 at 09:46:47AM +0800, Feng Tang wrote:
> Hi Qian,
>
> On Tue, May 26, 2020 at 02:14:59PM -0400, Qian Cai wrote:
> > On Thu, May 21, 2020 at 05:27:26PM -0400, Qian Cai wrote:
> > > On Fri, May 08, 2020 at 03:25:14PM +0800, Feng Tang wrote:
> > > > When checking a performance change for will-it-scale scalability
> > > > mmap test [1], we found very high lock contention for spinlock of
> > > > percpu counter 'vm_committed_as':
> > > >
> > > > 94.14% 0.35% [kernel.kallsyms] [k] _raw_spin_lock_irqsave
> > > > 48.21% _raw_spin_lock_irqsave;percpu_counter_add_batch;__vm_enough_memory;mmap_region;do_mmap;
> > > > 45.91% _raw_spin_lock_irqsave;percpu_counter_add_batch;__do_munmap;
> > > >
> > > > Actually this heavy lock contention is not always necessary. The
> > > > 'vm_committed_as' needs to be very precise when the strict
> > > > OVERCOMMIT_NEVER policy is set, which requires a rather small batch
> > > > number for the percpu counter.
> > > >
> > > > So lift the batch number to 16X for OVERCOMMIT_ALWAYS and
> > > > OVERCOMMIT_GUESS policies, and add a sysctl handler to adjust it
> > > > when the policy is reconfigured.
> > > >
> > > > Benchmark with the same testcase in [1] shows 53% improvement on a
> > > > 8C/16T desktop, and 2097%(20X) on a 4S/72C/144T server. And no change
> > > > for some platforms, due to the test mmap size of the case is bigger
> > > > than the batch number computed, though the patch will help mmap/munmap
> > > > generally.
> > > >
> > > > [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

# 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