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Date: Thu, 04 Jan 2018 23:31:12 -0700
From: "Gang He" <ghe@suse.com>
To: <jlbec@evilplan.org>, <jiangqi903@gmail.com>,
        <akpm@linux-foundation.org>, <mfasheh@versity.com>
Cc: <ocfs2-devel@oss.oracle.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH v2] ocfs2: try a blocking lock before
 return AOP_TRUNCATED_PAGE
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 <cb310814-4ad9-d3f3-674d-8746fae35fe0@gmail.com>
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Hi Andrew,

Happy new year.
Could you help to pick up this patch, which is used to fix a old patch 1cce4df04f37.
If we have not this patch, some multiple node test cases will trigger softlockup problems,
also make HA communication daemon (e.g. corosync) timeout and the node will has to be fenced.

Thanks
Gang  


>>> 

> 
> On 17/12/28 15:48, Gang He wrote:
>> If we can't get inode lock immediately in the function
>> ocfs2_inode_lock_with_page() when reading a page, we should not
>> return directly here, since this will lead to a softlockup problem
>> when the kernel is configured with CONFIG_PREEMPT is not set.
>> The method is to get a blocking lock and immediately unlock before
>> returning, this can avoid CPU resource waste due to lots of retries,
>> and benefits fairness in getting lock among multiple nodes, increase
>> efficiency in case modifying the same file frequently from multiple
>> nodes.
>> The softlockup crash (when set /proc/sys/kernel/softlockup_panic to 1)
>> looks like,
>> Kernel panic - not syncing: softlockup: hung tasks
>> CPU: 0 PID: 885 Comm: multi_mmap Tainted: G L 4.12.14-6.1-default #1
>> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>> Call Trace:
>>   <IRQ>
>>   dump_stack+0x5c/0x82
>>   panic+0xd5/0x21e
>>   watchdog_timer_fn+0x208/0x210
>>   ? watchdog_park_threads+0x70/0x70
>>   __hrtimer_run_queues+0xcc/0x200
>>   hrtimer_interrupt+0xa6/0x1f0
>>   smp_apic_timer_interrupt+0x34/0x50
>>   apic_timer_interrupt+0x96/0xa0
>>   </IRQ>
>>  RIP: 0010:unlock_page+0x17/0x30
>>  RSP: 0000:ffffaf154080bc88 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10
>>  RAX: dead000000000100 RBX: fffff21e009f5300 RCX: 0000000000000004
>>  RDX: dead0000000000ff RSI: 0000000000000202 RDI: fffff21e009f5300
>>  RBP: 0000000000000000 R08: 0000000000000000 R09: ffffaf154080bb00
>>  R10: ffffaf154080bc30 R11: 0000000000000040 R12: ffff993749a39518
>>  R13: 0000000000000000 R14: fffff21e009f5300 R15: fffff21e009f5300
>>   ocfs2_inode_lock_with_page+0x25/0x30 [ocfs2]
>>   ocfs2_readpage+0x41/0x2d0 [ocfs2]
>>   ? pagecache_get_page+0x30/0x200
>>   filemap_fault+0x12b/0x5c0
>>   ? recalc_sigpending+0x17/0x50
>>   ? __set_task_blocked+0x28/0x70
>>   ? __set_current_blocked+0x3d/0x60
>>   ocfs2_fault+0x29/0xb0 [ocfs2]
>>   __do_fault+0x1a/0xa0
>>   __handle_mm_fault+0xbe8/0x1090
>>   handle_mm_fault+0xaa/0x1f0
>>   __do_page_fault+0x235/0x4b0
>>   trace_do_page_fault+0x3c/0x110
>>   async_page_fault+0x28/0x30
>>  RIP: 0033:0x7fa75ded638e
>>  RSP: 002b:00007ffd6657db18 EFLAGS: 00010287
>>  RAX: 000055c7662fb700 RBX: 0000000000000001 RCX: 000055c7662fb700
>>  RDX: 0000000000001770 RSI: 00007fa75e909000 RDI: 000055c7662fb700
>>  RBP: 0000000000000003 R08: 000000000000000e R09: 0000000000000000
>>  R10: 0000000000000483 R11: 00007fa75ded61b0 R12: 00007fa75e90a770
>>  R13: 000000000000000e R14: 0000000000001770 R15: 0000000000000000
>> 
>> About performance improvement, we can see the testing time is reduced,
>> and CPU utilization decreases, the detailed data is as follows.
>> I ran multi_mmap test case in ocfs2-test package in a three nodes cluster.
>> Before apply this patch,
>>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>>  2754 ocfs2te+  20   0  170248   6980   4856 D 80.73 0.341   0:18.71 
> multi_mmap
>>  1505 root      rt   0  222236 123060  97224 S 2.658 6.015   0:01.44 
> corosync
>>     5 root      20   0       0      0      0 S 1.329 0.000   0:00.19 
> kworker/u8:0
>>    95 root      20   0       0      0      0 S 1.329 0.000   0:00.25 
> kworker/u8:1
>>  2728 root      20   0       0      0      0 S 0.997 0.000   0:00.24 
> jbd2/sda1-33
>>  2721 root      20   0       0      0      0 S 0.664 0.000   0:00.07 
> ocfs2dc-3C8CFD4
>>  2750 ocfs2te+  20   0  142976   4652   3532 S 0.664 0.227   0:00.28 mpirun
>> 
>> ocfs2test@tb-node2:~>multiple_run.sh -i ens3 -k ~/linux-4.4.21-69.tar.gz -o 
>> ~/ocfs2mullog -C hacluster -s pcmk -n tb-node2,tb-node1,tb-node3 -d 
>> /dev/sda1 -b 4096 -c 32768 -t multi_mmap /mnt/shared
>> Tests with "-b 4096 -C 32768"
>> Thu Dec 28 14:44:52 CST 2017
>> multi_mmap..................................................Passed.
>> Runtime 783 seconds.
>> 
>> After apply this patch,
>>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>>  2508 ocfs2te+  20   0  170248   6804   4680 R 54.00 0.333   0:55.37 
> multi_mmap
>>   155 root      20   0       0      0      0 S 2.667 0.000   0:01.20 
> kworker/u8:3
>>    95 root      20   0       0      0      0 S 2.000 0.000   0:01.58 
> kworker/u8:1
>>  2504 ocfs2te+  20   0  142976   4604   3480 R 1.667 0.225   0:01.65 mpirun
>>     5 root      20   0       0      0      0 S 1.000 0.000   0:01.36 
> kworker/u8:0
>>  2482 root      20   0       0      0      0 S 1.000 0.000   0:00.86 
> jbd2/sda1-33
>>   299 root       0 -20       0      0      0 S 0.333 0.000   0:00.13 
> kworker/2:1H
>>   335 root       0 -20       0      0      0 S 0.333 0.000   0:00.17 
> kworker/1:1H
>>   535 root      20   0   12140   7268   1456 S 0.333 0.355   0:00.34 haveged
>>  1282 root      rt   0  222284 123108  97224 S 0.333 6.017   0:01.33 
> corosync
>> 
>> ocfs2test@tb-node2:~>multiple_run.sh -i ens3 -k ~/linux-4.4.21-69.tar.gz -o 
>> ~/ocfs2mullog -C hacluster -s pcmk -n tb-node2,tb-node1,tb-node3 -d 
>> /dev/sda1 -b 4096 -c 32768 -t multi_mmap /mnt/shared
>> Tests with "-b 4096 -C 32768"
>> Thu Dec 28 15:04:12 CST 2017
>> multi_mmap..................................................Passed.
>> Runtime 487 seconds.
>> 
>> Fixes: 1cce4df04f37 ("ocfs2: do not lock/unlock() inode DLM lock")
>> Signed-off-by: Gang He <ghe@suse.com>
> Reviewed-by: Joseph Qi <jiangqi903@gmail.com>
> 
>> ---
>>  fs/ocfs2/dlmglue.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>> 
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 4689940..5193218 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -2486,6 +2486,15 @@ int ocfs2_inode_lock_with_page(struct inode *inode,
>>  	ret = ocfs2_inode_lock_full(inode, ret_bh, ex, OCFS2_LOCK_NONBLOCK);
>>  	if (ret == -EAGAIN) {
>>  		unlock_page(page);
>> +		/*
>> +		 * If we can't get inode lock immediately, we should not return
>> +		 * directly here, since this will lead to a softlockup problem.
>> +		 * The method is to get a blocking lock and immediately unlock
>> +		 * before returning, this can avoid CPU resource waste due to
>> +		 * lots of retries, and benefits fairness in getting lock.
>> +		 */
>> +		if (ocfs2_inode_lock(inode, ret_bh, ex) == 0)
>> +			ocfs2_inode_unlock(inode, ex);
>>  		ret = AOP_TRUNCATED_PAGE;
>>  	}
>>  
>>