Re: [f2fs-dev] [PATCH] f2fs: fix comment of f2fs_evict_inode

[Chao Yu]

On 2019/9/29 10:20, Gao Xiang wrote:
> On Sun, Sep 29, 2019 at 08:53:05AM +0800, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2019/9/28 2:31, Jaegeuk Kim wrote:
>>> Hi Chao,
>>>
>>> On 09/25, Chao Yu wrote:
>>>> evict() should be called once i_count is zero, rather than i_nlinke
>>>> is zero.
>>>>
>>>> Reported-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
>>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>>> ---
>>>>  fs/f2fs/inode.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>> index db4fec30c30d..8262f4a483d3 100644
>>>> --- a/fs/f2fs/inode.c
>>>> +++ b/fs/f2fs/inode.c
>>>> @@ -632,7 +632,7 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)
>>>>  }
>>>>  
>>>>  /*
>>>> - * Called at the last iput() if i_nlink is zero
>>>
>>> I don't think this comment is wrong. You may be able to add on top of this.
>>
>> It actually misleads the developer or user.
>>
>> How do you think of:
>>
>> "Called at the last iput() if i_count is zero, and will release all meta/data
>> blocks allocated in the inode if i_nlink is zero"
> 
> (sigh... side note: I just took some time to check the original meaning
>  out of curiosity. AFAIK, the above word was added in Linux-2.1.45 [1]
>  due to ext2_delete_inode behavior, which is called when i_nlink == 0,
>  and .delete_inode was gone in 2010 (commit 72edc4d0873b merge ext2
>  delete_inode and clear_inode, switch to ->evict_inode()), it may be
>  helpful to understand the story so I write here for later folks reference.
>  And it's also good to just kill it. )

Xiang,

Thanks for providing tracked info, I guess it's due to historical reason, we
kept the wrong comments in f2fs, anyway I agree that it should be fixed in
ext*/f2fs codes, let me send patches to fix comment in ext* as well.

Thanks,

> 
> +
> +/*
> + * Called at the last iput() if i_nlink is zero.
> + */
> +void ext2_delete_inode (struct inode * inode)
> +{
> +	if (inode->i_ino == EXT2_ACL_IDX_INO ||
>  	    inode->i_ino == EXT2_ACL_DATA_INO)
>  		return;
>  	inode->u.ext2_i.i_dtime	= CURRENT_TIME;
> -	inode->i_dirt = 1;
> +	mark_inode_dirty(inode);
>  	ext2_update_inode(inode, IS_SYNC(inode));
>  	inode->i_size = 0;
>  	if (inode->i_blocks)
> @@ -248,7 +258,7 @@
>  	if (IS_SYNC(inode) || inode->u.ext2_i.i_osync)
>  		ext2_sync_inode (inode);
>  	else
> -		inode->i_dirt = 1;
> +		mark_inode_dirty(inode);
>  	return result;
>  }
> 
> +void iput(struct inode *inode)
>  {
> -	struct inode * inode = get_empty_inode();
> +	if (inode) {
> +		struct super_operations *op = NULL;
>  
> -	PIPE_BASE(*inode) = (char*)__get_free_page(GFP_USER);
> -	if (!(PIPE_BASE(*inode))) {
> -		iput(inode);
> -		return NULL;
> +		if (inode->i_sb && inode->i_sb->s_op)
> +			op = inode->i_sb->s_op;
> +		if (op && op->put_inode)
> +			op->put_inode(inode);
> +
> +		spin_lock(&inode_lock);
> +		if (!--inode->i_count) {
> +			if (!inode->i_nlink) {
> +				list_del(&inode->i_hash);
> +				INIT_LIST_HEAD(&inode->i_hash);
> +				if (op && op->delete_inode) {
> +					void (*delete)(struct inode *) = op->delete_inode;
> +					spin_unlock(&inode_lock);
> +					delete(inode);
> +					spin_lock(&inode_lock);
> +				}
> +			}
> +			if (list_empty(&inode->i_hash)) {
> +				list_del(&inode->i_list);
> +				list_add(&inode->i_list, &inode_unused);
> +			}
> +		}
> +		spin_unlock(&inode_lock);
>  	}
> 
> [1] https://www.kernel.org/pub/linux/kernel/v2.1/patch-2.1.45.xz
> 
> Thanks,
> Gao Xiang
> 
>>
>> Thanks,
>>
>>>
>>>> + * Called at the last iput() if i_count is zero
>>>>   */
>>>>  void f2fs_evict_inode(struct inode *inode)
>>>>  {
>>>> -- 
>>>> 2.18.0.rc1
>>> .
>>>
>>
>>
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> .
>