Re: [PATCH] fs/super.c: do not shrink fs slab during direct memory reclaim

From: Xue jiufei
Date: Tue Sep 02 2014 - 23:30:26 EST

Hi Junxiao
On 2014/9/3 9:38, Junxiao Bi wrote:
> Hi Jiufei,
> On 09/02/2014 05:03 PM, Xue jiufei wrote:
>> Hi, Dave
>> On 2014/9/2 7:51, Dave Chinner wrote:
>>> On Fri, Aug 29, 2014 at 05:57:22PM +0800, Xue jiufei wrote:
>>>> The patch trys to solve one deadlock problem caused by cluster
>>>> fs, like ocfs2. And the problem may happen at least in the below
>>>> situations:
>>>> 1)Receiving a connect message from other nodes, node queues a
>>>> work_struct o2net_listen_work.
>>>> 2)o2net_wq processes this work and calls sock_alloc() to allocate
>>>> memory for a new socket.
>>>> 3)It would do direct memory reclaim when available memory is not
>>>> enough and trigger the inode cleanup. That inode being cleaned up
>>>> is happened to be ocfs2 inode, so call evict()->ocfs2_evict_inode()
>>>> ->ocfs2_drop_lock()->dlmunlock()->o2net_send_message_vec(),
>>>> and wait for the unlock response from master.
>>>> 4)tcp layer received the response, call o2net_data_ready() and
>>>> queue sc_rx_work, waiting o2net_wq to process this work.
>>>> 5)o2net_wq is a single thread workqueue, it process the work one by
>>>> one. Right now it is still doing o2net_listen_work and cannot handle
>>>> sc_rx_work. so we deadlock.
>>>> It is impossible to set GFP_NOFS for memory allocation in sock_alloc().
>>>> So we use PF_FSTRANS to avoid the task reentering filesystem when
>>>> available memory is not enough.
>>>> Signed-off-by: joyce.xue <xuejiufei@xxxxxxxxxx>
>>> For the second time: use memalloc_noio_save/memalloc_noio_restore.
>>> And please put a great big comment in the code explaining why you
>>> need to do this special thing with memory reclaim flags.
>>> Cheers,
>>> Dave.
>> Thanks for your reply. But I am afraid that memalloc_noio_save/
>> memalloc_noio_restore can not solve my problem. __GFP_IO is cleared
>> if PF_MEMALLOC_NOIO is set and can avoid doing IO in direct memory
>> reclaim. However, __GFP_FS is still set that can not avoid pruning
>> dcache and icache in memory allocation, resulting in the deadlock I
>> described.
> You can use PF_MEMALLOC_NOIO to replace PF_FSTRANS, set this flag in
> ocfs2 and check it in sb shrinker.
Thanks for your advice. But I think using another process flag is better.
Do you think so? I will send another patch later.


> Thanks,
> Junxiao.

>> Thanks.
>> XueJiufei
> .

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