On Wed, Sep 03, 2014 at 12:21:24PM +0800, Junxiao Bi wrote: > On 09/03/2014 11:10 AM, Dave Chinner wrote: > > 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 <xuejiu...@huawei.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. > >>>> > >>> 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. > __GFP_FS seemed imply __GFP_IO,
Now you are starting to understand. Check what GFP_NOIO actually means, then tell me why memalloc_noio_flags() is not fully correct, needs fixing, and needs to be applied to all of reclaim. Hint: there's a heirarchy involved.... > can superblock shrinker check > !(sc->gfp_mask & __GFP_IO) and stop? No. Go back and read what I said about the initial setting of sc->gfp_mask. Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
