linux-kernel - Re: [Ocfs2-devel] [PATCH 1/3] ocfs2: add ocfs2_try_rw_lock and ocfs2_try_inode

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Message-ID: <63ADC13FD55D6546B7DECE290D39E373F146F95E@H3CMLB12-EX.srv.huawei-3com.com>
Date:   Tue, 28 Nov 2017 01:52:13 +0000
From:   Changwei Ge <ge.changwei@....com>
To:     Gang He <ghe@...e.com>,
        "mfasheh@...sity.com" <mfasheh@...sity.com>,
        "jlbec@...lplan.org" <jlbec@...lplan.org>,
        "rgoldwyn@...e.com" <rgoldwyn@...e.com>, "hch@....de" <hch@....de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH 1/3] ocfs2: add ocfs2_try_rw_lock and
 ocfs2_try_inode_lock

Hi Gang,

On 2017/11/27 17:48, 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 | 22 ++++++++++++++++++++++
>   fs/ocfs2/dlmglue.h |  4 ++++
>   2 files changed, 26 insertions(+)
> 
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 4689940..5cfbd04 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -1742,6 +1742,28 @@ 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(OCFS2_SB(inode->i_sb), lockres, level,
> +				    DLM_LKF_NOQUEUE, 0);
> +	return status;
> +}

The newly added function ocfs2_try_rw_lock almost has the same logic 
with ocfs2_rw_lock.Is it possible to combine them into an unique one?
That will be more elegant.

Moreover, can you elaborate further why we need a *NOQUEUE* lock for 
supporting non-block aio?

Why can't we wait for a while to grant a lock request? Is this necessary?

Thanks,
Changwei

> +
>   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,
>