fs/super.c: do not shrink fs slab during direct memory reclaim

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 <[email protected]>

---
 fs/ocfs2/cluster/tcp.c | 7 +++++++
 fs/super.c             | 3 +++
 2 files changed, 10 insertions(+)

fs/ocfs2/cluster/tcp.c +7 -0

index 681691b..629b4da 100644
@@ -1581,6 +1581,8 @@ static void o2net_start_connect(struct work_struct *work)
 	int ret = 0, stop;
 	unsigned int timeout;
 
+	current->flags |= PF_FSTRANS;
+
 	/* if we're greater we initiate tx, otherwise we accept */
 	if (o2nm_this_node() <= o2net_num_from_nn(nn))
 		goto out;

@@ -1683,6 +1685,7 @@ out:
 	if (mynode)
 		o2nm_node_put(mynode);
 
+	current->flags &= ~PF_FSTRANS;
 	return;
 }
 

@@ -1809,6 +1812,8 @@ static int o2net_accept_one(struct socket *sock, int *more)
 	struct o2net_sock_container *sc = NULL;
 	struct o2net_node *nn;
 
+	current->flags |= PF_FSTRANS;
+
 	BUG_ON(sock == NULL);
 	*more = 0;
 	ret = sock_create_lite(sock->sk->sk_family, sock->sk->sk_type,

@@ -1918,6 +1923,8 @@ out:
 		o2nm_node_put(local_node);
 	if (sc)
 		sc_put(sc);
+
+	current->flags &= ~PF_FSTRANS;
 	return ret;
 }
 

fs/super.c +3 -0

index b9a214d..c4a8dc1 100644
@@ -71,6 +71,9 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!(sc->gfp_mask & __GFP_FS))
 		return SHRINK_STOP;
 
+	if (current->flags & PF_FSTRANS)
+		return SHRINK_STOP;
+
 	if (!grab_super_passive(sb))
 		return SHRINK_STOP;
 

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 <[email protected]>

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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.

Hi, Dave

Quoted 29 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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.

Quoted 4 lines

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.

Quoted 31 lines · Xue jiufei

Hi, Dave

Quoted 29 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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.

Quoted 8 lines

Quoted 4 lines

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.

Well, yes. It sets a process flag that is used to avoid re-entrancy issues in direct reclaim. Direct reclaim is more than just the superblock shrinker - there are lots of other shrinkers, page reclaim, etc and I bet there are other paths that can trigger the deadlock you are seeing. We need to protect against all those cases, not just the one shrinker you see a problem with. i.e. we need to clear __GPF_FS from *all* reclaim, not just the superblock shrinker.

Also, PF_FSTRANS is used internally by filesystems, not the generic code. If we start spreading it through generic code like this, we start breaking filesystems that rely on it having a specific, filesystem internal meaning. So it's a NACK on that basis as well.

Quoted 3 lines

However, __GFP_FS is still set that can not avoid pruning dcache and icache in memory allocation, resulting in the deadlock I described.

You have a deadlock in direct reclaim, and we already have a template for setting a process flag that is used to indirectly control direct reclaim behaviour. If the current process flag doesn't provide precisely the coverage, then use that implementation as the template to do exactly what is needed for your case.

Cheers,

Dave.

Hi, Dave

Quoted 31 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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,

Quoted 2 lines

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.

Thanks.
XueJiufei

Hi Jiufei,

Quoted 33 lines · Xue jiufei

Hi, Dave

Quoted 31 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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,

Quoted 8 lines

Quoted 2 lines

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.

Quoted 45 lines · Junxiao Bi

Hi Jiufei,

Quoted 41 lines · Xue jiufei

Hi, Dave

Quoted 25 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

Quoted 8 lines

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.

Quoted 2 lines

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.

Quoted 46 lines · Dave Chinner

Quoted 45 lines · Junxiao Bi

Hi Jiufei,

Quoted 41 lines · Xue jiufei

Hi, Dave

Quoted 25 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

Quoted 8 lines

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.

Quoted 7 lines

Quoted 2 lines

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,

can superblock shrinker check
!(sc->gfp_mask & __GFP_IO) and stop?

Hi Jiufei,

Quoted 33 lines · Xue jiufei

Hi, Dave

Quoted 31 lines · Dave Chinner

Quoted 18 lines · Xue jiufei

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.

Quoted 5 lines

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 <[email protected]>

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,

Quoted 8 lines

Quoted 2 lines

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,
Junxiao.

Quoted 7 lines

Thanks.
XueJiufei

.