Re: [PATCH] mm: fix oom work when memory is under pressure

From: zhong jiang <zhongjiang@huawei.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: akpm@linux-foundation.org, vbabka@suse.cz, rientjes@google.com,
	linux-mm@kvack.org, Xishi Qiu <qiuxishi@huawei.com>,
	Hanjun Guo <guohanjun@huawei.com>
Subject: Re: [PATCH] mm: fix oom work when memory is under pressure
Date: Wed, 14 Sep 2016 16:50:48 +0800	[thread overview]
Message-ID: <57D90F68.4000100@huawei.com> (raw)
In-Reply-To: <20160914084219.GA1612@dhcp22.suse.cz>

On 2016/9/14 16:42, Michal Hocko wrote:
> [Let's CC Hugh]
>
> On Wed 14-09-16 15:13:50, zhong jiang wrote:
> [...]
>>   hi, Michal
>>
>>   Recently, I hit the same issue when run a OOM case of the LTP and ksm enable.
>>  
>> [  601.937145] Call trace:
>> [  601.939600] [<ffffffc000086a88>] __switch_to+0x74/0x8c
>> [  601.944760] [<ffffffc000a1bae0>] __schedule+0x23c/0x7bc
>> [  601.950007] [<ffffffc000a1c09c>] schedule+0x3c/0x94
>> [  601.954907] [<ffffffc000a1eb84>] rwsem_down_write_failed+0x214/0x350
>> [  601.961289] [<ffffffc000a1e32c>] down_write+0x64/0x80
>> [  601.966363] [<ffffffc00021f794>] __ksm_exit+0x90/0x19c
>> [  601.971523] [<ffffffc0000be650>] mmput+0x118/0x11c
>> [  601.976335] [<ffffffc0000c3ec4>] do_exit+0x2dc/0xa74
>> [  601.981321] [<ffffffc0000c46f8>] do_group_exit+0x4c/0xe4
>> [  601.986656] [<ffffffc0000d0f34>] get_signal+0x444/0x5e0
>> [  601.991904] [<ffffffc000089fcc>] do_signal+0x1d8/0x450
>> [  601.997065] [<ffffffc00008a35c>] do_notify_resume+0x70/0x78
> So this is a hung task triggering because the exiting task cannot get
> the mmap sem for write because the ksmd holds it for read while
> allocating memory which just takes ages to complete, right?
  Yes
>> The root case is that ksmd hold the read lock. and the lock is not released.
>>  scan_get_next_rmap_item
>>          down_read
>>                    get_next_rmap_item
>>                              alloc_rmap_item     #ksmd will loop permanently.
>>
>> How do you see this kind of situation ? or  let the issue alone.
> I am not familiar with the ksmd code so it is hard for me to judge but
> one thing to do would be __GFP_NORETRY which would force a bail out from
> the allocation rather than looping for ever. A quick look tells me that
> the allocation failure here is quite easy to handle. There might be
> others...
>
  by adding my patch , The question is fixed.  They are same issue.

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