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

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

[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.

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

diff --git a/fs/ocfs2/cluster/tcp.c b/fs/ocfs2/cluster/tcp.c
index 681691b..629b4da 100644
--- a/fs/ocfs2/cluster/tcp.c
+++ b/fs/ocfs2/cluster/tcp.c
@@ -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;
 }
 
diff --git a/fs/super.c b/fs/super.c
index b9a214d..c4a8dc1 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -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;
 
-- 
1.8.4.3

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

[Xue jiufei]

Hi Viro & Andraw
Could you help review this patch?

Thanks.
xuejiufei

On 2014/8/29 17:57, 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@huawei.com>
> ---
>  fs/ocfs2/cluster/tcp.c | 7 +++++++
>  fs/super.c             | 3 +++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/fs/ocfs2/cluster/tcp.c b/fs/ocfs2/cluster/tcp.c
> index 681691b..629b4da 100644
> --- a/fs/ocfs2/cluster/tcp.c
> +++ b/fs/ocfs2/cluster/tcp.c
> @@ -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;
>  }
>  
> diff --git a/fs/super.c b/fs/super.c
> index b9a214d..c4a8dc1 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -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;
> 
> 

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

[Dave Chinner]

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@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.
-- 
Dave Chinner
david@fromorbit.com

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

[Xue jiufei]

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@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.

Thanks.
XueJiufei



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

[Dave Chinner]

On Tue, Sep 02, 2014 at 05:03:27PM +0800, 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@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.

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.

> 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.
-- 
Dave Chinner
david@fromorbit.com

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

[Xue jiufei]

Hi, Dave
On 2014/9/3 9:02, Dave Chinner wrote:
> On Tue, Sep 02, 2014 at 05:03:27PM +0800, 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@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.
> 
> 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.
> 
>> 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.
> 
Thanks very much for your advise. I will send another patch later.

Thanks,
Xuejiufei

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

[Junxiao Bi]

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@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.

Thanks,
Junxiao.
> 
> Thanks.
> XueJiufei
> 
> 
> 

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

[Dave Chinner]

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@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.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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

[Junxiao Bi]

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

Thanks,
Junxiao.
> 
> Cheers,
> 
> Dave.
> 

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

[Dave Chinner]

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 <xuejiufei@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
david@fromorbit.com

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

[Xue jiufei]

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@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.
> 
Thanks for your advice. But I think using another process flag is better.
Do you think so? I will send another patch later.

Thanks,
XueJiufei 

> Thanks,
> Junxiao.
>>

>> Thanks.
>> XueJiufei
>>
>>
>>
> 
> .
>