On Wed, Sep 03, 2014 at 09:38:31AM +0800, 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. No changes to the superblock shrinker, please. The flag should modify the gfp_mask in the struct shrink_control passed to the shrinker, just like the noio flag is used in the rest of the mm code. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
