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

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Date:	Tue, 2 Sep 2014 09:51:02 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Xue jiufei <xuejiufei@...wei.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	"ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
	Junxiao Bi <junxiao.bi@...cle.com>
Subject: Re: [PATCH] fs/super.c: do not shrink fs slab during direct memory
 reclaim

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@...wei.com>

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.
-- 
Dave Chinner
david@...morbit.com
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