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Message-Id: <5A1FE111020000F90009B606@prv-mh.provo.novell.com>
Date: Wed, 29 Nov 2017 19:44:33 -0700
From: "Gang He" <ghe@...e.com>
To: <jlbec@...lplan.org>, <ge.changwei@....com>, <hch@....de>,
"Goldwyn Rodrigues" <RGoldwyn@...e.com>, <mfasheh@...sity.com>
Cc: <ocfs2-devel@....oracle.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH v2 1/3] ocfs2: add ocfs2_try_rw_lock
and ocfs2_try_inode_lock
Hello Changwei,
>>>
> On 2017/11/29 16:38, Gang He wrote:
>> Add ocfs2_try_rw_lock and ocfs2_try_inode_lock functions, which
>> will be used in non-block IO scenarios.
>>
>> Signed-off-by: Gang He <ghe@...e.com>
>> ---
>> fs/ocfs2/dlmglue.c | 21 +++++++++++++++++++++
>> fs/ocfs2/dlmglue.h | 4 ++++
>> 2 files changed, 25 insertions(+)
>>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 4689940..a68efa3 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -1742,6 +1742,27 @@ int ocfs2_rw_lock(struct inode *inode, int write)
>> return status;
>> }
>>
>> +int ocfs2_try_rw_lock(struct inode *inode, int write)
>> +{
>> + int status, level;
>> + struct ocfs2_lock_res *lockres;
>> + struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>> +
>> + mlog(0, "inode %llu try to take %s RW lock\n",
>> + (unsigned long long)OCFS2_I(inode)->ip_blkno,
>> + write ? "EXMODE" : "PRMODE");
>> +
>> + if (ocfs2_mount_local(osb))
>> + return 0;
>> +
>> + lockres = &OCFS2_I(inode)->ip_rw_lockres;
>> +
>> + level = write ? DLM_LOCK_EX : DLM_LOCK_PR;
>> +
>> + status = ocfs2_cluster_lock(osb, lockres, level, DLM_LKF_NOQUEUE, 0);
>
> Hi Gang,
> Should we consider about passing a flag - OCFS2_LOCK_NONBLOCK to
> ocfs2_cluster_lock. Otherwise a cluster locking progress may be waiting
> for accomplishment of DC, which I think violates _NO_WAIT_ semantics.
If ocfs2 is a local file system, we should not wait for any condition, but for a cluster file system,
we cannot avoid this totally according to the current DLM lock design, we need to wait for a little to get lock for the first time.
Why do we not use OCFS2_LOCK_NONBLOCK flag to get a lock?
since this flag is not stable to get a lock no matter this lock is occupied by other nodes, or not.
If you use OCFS2_LOCK_NONBLOCK flag to get a fresh lock, you possibly fail or success, depends on when the lock acquisition callback happens.
So, I think DLM_LKF_NOQUEUE flag should be more matched to _NO_WAIT_ semantics.
we always get a fresh lock successfully, always failed if the lock is/was occupied by other nodes.
This flag can give us a consistent locking behavior.
Thanks
Gang
>
> Thanks,
> Changwei.
>
>> + return status;
>> +}
>> +
>> void ocfs2_rw_unlock(struct inode *inode, int write)
>> {
>> int level = write ? DLM_LOCK_EX : DLM_LOCK_PR;
>> diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h
>> index a7fc18b..05910fc 100644
>> --- a/fs/ocfs2/dlmglue.h
>> +++ b/fs/ocfs2/dlmglue.h
>> @@ -116,6 +116,7 @@ void ocfs2_refcount_lock_res_init(struct ocfs2_lock_res
> *lockres,
>> int ocfs2_create_new_inode_locks(struct inode *inode);
>> int ocfs2_drop_inode_locks(struct inode *inode);
>> int ocfs2_rw_lock(struct inode *inode, int write);
>> +int ocfs2_try_rw_lock(struct inode *inode, int write);
>> void ocfs2_rw_unlock(struct inode *inode, int write);
>> int ocfs2_open_lock(struct inode *inode);
>> int ocfs2_try_open_lock(struct inode *inode, int write);
>> @@ -140,6 +141,9 @@ int ocfs2_inode_lock_with_page(struct inode *inode,
>> /* 99% of the time we don't want to supply any additional flags --
>> * those are for very specific cases only. */
>> #define ocfs2_inode_lock(i, b, e) ocfs2_inode_lock_full_nested(i, b, e, 0,
> OI_LS_NORMAL)
>> +#define ocfs2_try_inode_lock(i, b, e)\
>> + ocfs2_inode_lock_full_nested(i, b, e, OCFS2_META_LOCK_NOQUEUE,\
>> + OI_LS_NORMAL)
>> void ocfs2_inode_unlock(struct inode *inode,
>> int ex);
>> int ocfs2_super_lock(struct ocfs2_super *osb,
>>
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